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Re: [PATCH v8 3/3] tpm: Add support for TPM device over I2C bus


From: Cédric Le Goater
Subject: Re: [PATCH v8 3/3] tpm: Add support for TPM device over I2C bus
Date: Mon, 27 Mar 2023 19:01:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0

On 3/27/23 18:16, Ninad Palsule wrote:
Qemu already supports devices attached to ISA and sysbus. This drop adds
support for the I2C bus attached TPM devices. I2C model only supports
TPM2 protocol.

This commit includes changes for the common code.
- Added I2C emulation model. Logic was added in the model to temporarily
   cache the data as I2C interface works per byte basis.
- New tpm type "tpm-tis-i2c" added for I2C support. The user has to
   provide this string on command line.

Testing:
   TPM I2C device module is tested using SWTPM (software based TPM
   package). Qemu uses the rainier machine and is connected to swtpm over
   the socket interface.

   The command to start swtpm is as follows:
   $ swtpm socket --tpmstate dir=/tmp/mytpm1    \
                  --ctrl type=unixio,path=/tmp/mytpm1/swtpm-sock  \
                  --tpm2 --log level=100

   The command to start qemu is as follows:
   $ qemu-system-arm -M rainier-bmc -nographic \
             -kernel ${IMAGEPATH}/fitImage-linux.bin \
             -dtb ${IMAGEPATH}/aspeed-bmc-ibm-rainier.dtb \
             -initrd ${IMAGEPATH}/obmc-phosphor-initramfs.rootfs.cpio.xz \
             -drive 
file=${IMAGEPATH}/obmc-phosphor-image.rootfs.wic.qcow2,if=sd,index=2 \
             -net nic -net 
user,hostfwd=:127.0.0.1:2222-:22,hostfwd=:127.0.0.1:2443-:443 \
             -chardev socket,id=chrtpm,path=/tmp/mytpm1/swtpm-sock \
             -tpmdev emulator,id=tpm0,chardev=chrtpm \
             -device tpm-tis-i2c,tpmdev=tpm0,bus=aspeed.i2c.bus.12,address=0x2e

Signed-off-by: Ninad Palsule <ninad@linux.ibm.com>
---
V2:
Incorporated Stephen's review comments.
- Handled checksum related register in I2C layer
- Defined I2C interface capabilities and return those instead of
   capabilities from TPM TIS. Add required capabilities from TIS.
- Do not cache FIFO data in the I2C layer.
- Make sure that Device address change register is not passed to I2C
   layer as capability indicate that it is not supported.
- Added boundary checks.
- Make sure that bits 26-31 are zeroed for the TPM_STS register on read
- Updated Kconfig files for new define.

---
V3:
- Moved processing of register TPM_I2C_LOC_SEL in the I2C. So I2C layer
   remembers the locality and pass it to TIS on each read/write.
- The write data is no more cached in the I2C layer so the buffer size
   is reduced to 16 bytes.
- Checksum registers are now managed by the I2C layer. Added new
   function in TIS layer to return the checksum and used that to process
   the request.
- Now 2-4 byte register value will be passed to TIS layer in a single
   write call instead of 1 byte at a time. Added functions to convert
   between little endian stream of bytes to single 32 bit unsigned
   integer. Similarly 32  bit integer to stream of bytes.
- Added restriction on device change register.
- Replace few if-else statement with switch statement for clarity.
- Log warning when unknown register is received.
- Moved all register definations to acpi/tmp.h

---
V4:
Incorporated review comments from Cedric and Stefan.
- Reduced data[] size from 16 byte to 5 bytes.
- Added register name in the mapping table which can be used for
   tracing.
- Removed the endian conversion functions instead used simple logic
   provided by Stefan.
- Rename I2C registers to reduce the length.
- Added traces for send, recv and event functions. You can turn on trace
   on command line by using "-trace "tpm_tis_i2c*" option.

---
V5:
Fixed issues reported by Stefan's test.
- Added mask for the INT_ENABLE register.
- Use correct TIS register for reading interrupt capability.
- Cleanup how register is converted from I2C to TIS and also saved
   information like tis_addr and register name in the i2cst so that we
   can only convert it once on i2c_send.
- Trace register number for unknown registers.

---
V6:
Fixed review comments from Stefan.
- Fixed some variable size.
- Removed unused variables.
- Added vmstat backin to handle migration.
- Added post load phase to reload tis address and register name.

---
V7:
Incorporated review comments from Stefan.
- Added tpm_tis_i2c_initfn function
- Set the device catagory DEVICE_CATEGORY_MISC.
- Corrected default locality selection.
- Other cleanup. Include file cleanup.

---
V8:
Incorporated review comments from Stefan.
- Removed the irq initialization as linux doesn't support interrupts for
   TPM
- Handle INT_CAPABILITY register in I2C only and return 0 to indicate
   that it is not supported.
---
  hw/arm/Kconfig       |   1 +
  hw/tpm/Kconfig       |   7 +
  hw/tpm/meson.build   |   1 +
  hw/tpm/tpm_tis_i2c.c | 525 +++++++++++++++++++++++++++++++++++++++++++
  hw/tpm/trace-events  |   6 +
  include/sysemu/tpm.h |   3 +
  6 files changed, 543 insertions(+)
  create mode 100644 hw/tpm/tpm_tis_i2c.c

diff --git a/hw/arm/Kconfig b/hw/arm/Kconfig
index b5aed4aff5..05d6ef1a31 100644
--- a/hw/arm/Kconfig
+++ b/hw/arm/Kconfig
@@ -6,6 +6,7 @@ config ARM_VIRT
      imply VFIO_PLATFORM
      imply VFIO_XGMAC
      imply TPM_TIS_SYSBUS
+    imply TPM_TIS_I2C
      imply NVDIMM
      select ARM_GIC
      select ACPI
diff --git a/hw/tpm/Kconfig b/hw/tpm/Kconfig
index 29e82f3c92..a46663288c 100644
--- a/hw/tpm/Kconfig
+++ b/hw/tpm/Kconfig
@@ -1,3 +1,10 @@
+config TPM_TIS_I2C
+    bool
+    depends on TPM
+    select TPM_BACKEND
+    select I2C
+    select TPM_TIS
+
  config TPM_TIS_ISA
      bool
      depends on TPM && ISA_BUS
diff --git a/hw/tpm/meson.build b/hw/tpm/meson.build
index 7abc2d794a..76fe3cb098 100644
--- a/hw/tpm/meson.build
+++ b/hw/tpm/meson.build
@@ -1,6 +1,7 @@
  softmmu_ss.add(when: 'CONFIG_TPM_TIS', if_true: files('tpm_tis_common.c'))
  softmmu_ss.add(when: 'CONFIG_TPM_TIS_ISA', if_true: files('tpm_tis_isa.c'))
  softmmu_ss.add(when: 'CONFIG_TPM_TIS_SYSBUS', if_true: 
files('tpm_tis_sysbus.c'))
+softmmu_ss.add(when: 'CONFIG_TPM_TIS_I2C', if_true: files('tpm_tis_i2c.c'))
  softmmu_ss.add(when: 'CONFIG_TPM_CRB', if_true: files('tpm_crb.c'))
  softmmu_ss.add(when: 'CONFIG_TPM_TIS', if_true: files('tpm_ppi.c'))
  softmmu_ss.add(when: 'CONFIG_TPM_CRB', if_true: files('tpm_ppi.c'))
diff --git a/hw/tpm/tpm_tis_i2c.c b/hw/tpm/tpm_tis_i2c.c
new file mode 100644
index 0000000000..5bbc414753
--- /dev/null
+++ b/hw/tpm/tpm_tis_i2c.c
@@ -0,0 +1,525 @@
+/*
+ * tpm_tis_i2c.c - QEMU's TPM TIS I2C Device


missing Copyright here ?


+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ * Implementation of the TIS interface according to specs found at
+ * http://www.trustedcomputinggroup.org. This implementation currently
+ * supports version 1.3, 21 March 2013
+ * In the developers menu choose the PC Client section then find the TIS
+ * specification.
+ *
+ * TPM TIS for TPM 2 implementation following TCG PC Client Platform
+ * TPM Profile (PTP) Specification, Familiy 2.0, Revision 00.43
+ *
+ * TPM I2C implementation follows TCG TPM I2c Interface specification,
+ * Family 2.0, Level 00, Revision 1.00
+ */
+
+#include "qemu/osdep.h"
+#include "hw/i2c/i2c.h"
+#include "hw/sysbus.h"
+#include "hw/acpi/tpm.h"
+#include "migration/vmstate.h"
+#include "tpm_prop.h"
+#include "qemu/log.h"
+#include "trace.h"
+#include "tpm_tis.h"
+
+/* TPM_STS mask for read bits 31:26 must be zero */
+#define TPM_I2C_STS_READ_MASK          0x03ffffff
+
+/* Operations */
+#define OP_SEND   1
+#define OP_RECV   2
+
+typedef struct TPMStateI2C {
+    /*< private >*/
+    I2CSlave    parent_obj;
+
+    uint8_t     offset;       /* offset into data[] */
+    uint8_t     operation;    /* OP_SEND & OP_RECV */
+    uint8_t     data[5];      /* Data */
+
+    /* i2c registers */
+    uint8_t     loc_sel;      /* Current locality */
+    uint8_t     csum_enable;  /* Is checksum enabled */
+
+    /* Derived from the above */
+    const char *reg_name;     /* Register name */
+    uint32_t    tis_addr;     /* Converted tis address including locty */
+
+    /*< public >*/
+    TPMState    state; /* not a QOM object */
+
+} TPMStateI2C;
+
+DECLARE_INSTANCE_CHECKER(TPMStateI2C, TPM_TIS_I2C,
+                         TYPE_TPM_TIS_I2C)
+
+/* Prototype */
+static inline void tpm_tis_i2c_to_tis_reg(TPMStateI2C *i2cst, uint8_t i2c_reg);
+
+/* Register map */
+typedef struct regMap {
+    uint8_t   i2c_reg;    /* I2C register */
+    uint16_t  tis_reg;    /* TIS register */
+    const char *reg_name; /* Register name */
+} I2CRegMap;
+
+/*
+ * The register values in the common code is different than the latest
+ * register numbers as per the spec hence add the conversion map
+ */
+static const I2CRegMap tpm_tis_reg_map[] = {
+    /*
+     * These registers are sent to TIS layer. The register with UNKNOWN
+     * mapping are not sent to TIS layer and handled in I2c layer.
+     * NOTE: Adding frequently used registers at the start
+     */
+    { TPM_I2C_REG_DATA_FIFO,        TPM_TIS_REG_DATA_FIFO,       "FIFO",      
},
+    { TPM_I2C_REG_STS,              TPM_TIS_REG_STS,             "STS",       
},
+    { TPM_I2C_REG_DATA_CSUM_GET,    TPM_I2C_REG_UNKNOWN,         "CSUM_GET",  
},
+    { TPM_I2C_REG_LOC_SEL,          TPM_I2C_REG_UNKNOWN,         "LOC_SEL",   
},
+    { TPM_I2C_REG_ACCESS,           TPM_TIS_REG_ACCESS,          "ACCESS",    
},
+    { TPM_I2C_REG_INT_ENABLE,       TPM_TIS_REG_INT_ENABLE,     
"INTR_ENABLE",},
+    { TPM_I2C_REG_INT_CAPABILITY,   TPM_I2C_REG_UNKNOWN,         "INTR_CAP",  
},
+    { TPM_I2C_REG_INTF_CAPABILITY,  TPM_TIS_REG_INTF_CAPABILITY, "INTF_CAP",  
},
+    { TPM_I2C_REG_DID_VID,          TPM_TIS_REG_DID_VID,         "DID_VID",   
},
+    { TPM_I2C_REG_RID,              TPM_TIS_REG_RID,             "RID",       
},
+    { TPM_I2C_REG_I2C_DEV_ADDRESS,  TPM_I2C_REG_UNKNOWN,        
"DEV_ADDRESS",},
+    { TPM_I2C_REG_DATA_CSUM_ENABLE, TPM_I2C_REG_UNKNOWN,        
"CSUM_ENABLE",},
+};
+
+static int tpm_tis_i2c_pre_save(void *opaque)
+{
+    TPMStateI2C *i2cst = opaque;
+
+    return tpm_tis_pre_save(&i2cst->state);
+}
+
+static int tpm_tis_i2c_post_load(void *opaque, int version_id)
+{
+    TPMStateI2C *i2cst = opaque;
+
+    if (i2cst->offset >= 1) {
+        tpm_tis_i2c_to_tis_reg(i2cst, i2cst->data[0]);
+    }
+
+    return 0;
+}
+
+static const VMStateDescription vmstate_tpm_tis_i2c = {
+    .name = "tpm-tis-i2c",
+    .version_id = 0,
+    .pre_save  = tpm_tis_i2c_pre_save,
+    .post_load  = tpm_tis_i2c_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_BUFFER(state.buffer, TPMStateI2C),
+        VMSTATE_UINT16(state.rw_offset, TPMStateI2C),
+        VMSTATE_UINT8(state.active_locty, TPMStateI2C),
+        VMSTATE_UINT8(state.aborting_locty, TPMStateI2C),
+        VMSTATE_UINT8(state.next_locty, TPMStateI2C),
+
+        VMSTATE_STRUCT_ARRAY(state.loc, TPMStateI2C, TPM_TIS_NUM_LOCALITIES, 0,
+                             vmstate_locty, TPMLocality),
+
+        /* i2c specifics */
+        VMSTATE_UINT8(offset, TPMStateI2C),
+        VMSTATE_UINT8(operation, TPMStateI2C),
+        VMSTATE_BUFFER(data, TPMStateI2C),
+        VMSTATE_UINT8(loc_sel, TPMStateI2C),
+        VMSTATE_UINT8(csum_enable, TPMStateI2C),
+
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+/*
+ * Generate interface capability based on what is returned by TIS and what is
+ * expected by I2C. Save the capability in the data array overwriting the TIS
+ * capability.
+ */
+static uint32_t tpm_i2c_interface_capability(TPMStateI2C *i2cst,
+                                             uint32_t tis_cap)
+{
+    uint32_t i2c_cap;
+
+    /* Now generate i2c capability */
+    i2c_cap = (TPM_I2C_CAP_INTERFACE_TYPE |
+               TPM_I2C_CAP_INTERFACE_VER  |
+               TPM_I2C_CAP_TPM2_FAMILY    |
+               TPM_I2C_CAP_LOCALITY_CAP   |
+               TPM_I2C_CAP_BUS_SPEED      |
+               TPM_I2C_CAP_DEV_ADDR_CHANGE);
+
+    /* Now check the TIS and set some capabilities */
+
+    /* Static burst count set */
+    if (tis_cap & TPM_TIS_CAP_BURST_COUNT_STATIC) {
+        i2c_cap |= TPM_I2C_CAP_BURST_COUNT_STATIC;
+    }
+
+    return i2c_cap;
+}
+
+/* Convert I2C register to TIS address and returns the name of the register */
+static inline void tpm_tis_i2c_to_tis_reg(TPMStateI2C *i2cst, uint8_t i2c_reg)
+{
+    const I2CRegMap *reg_map;
+    int i;
+
+    i2cst->tis_addr = 0xffffffff;
+
+    for (i = 0; i < ARRAY_SIZE(tpm_tis_reg_map); i++) {
+        reg_map = &tpm_tis_reg_map[i];
+        if (reg_map->i2c_reg == i2c_reg) {
+            i2cst->reg_name = reg_map->reg_name;
+            i2cst->tis_addr = reg_map->tis_reg;
+            if (i2cst->loc_sel != TPM_TIS_NO_LOCALITY) {
+                /* Include the locality in the address. */
+                i2cst->tis_addr += (i2cst->loc_sel << TPM_TIS_LOCALITY_SHIFT);
+            }
+            break;
+        }
+    }
+
+    if (i2cst->tis_addr == 0xffffffff) {
+        qemu_log_mask(LOG_UNIMP, "%s: Could not convert i2c register: 0x%X\n",
+                      __func__, i2cst->data[0]);

This condition looks more like a guest error to me. Doesn't it ?

+    }
+}
+
+/* Clear some fields from the structure. */
+static inline void tpm_tis_i2c_clear_data(TPMStateI2C *i2cst)
+{
+    /* Clear operation and offset */
+    i2cst->operation = 0;
+    i2cst->offset = 0;
+    i2cst->tis_addr = 0xffffffff;
+    i2cst->reg_name = NULL;
+    memset(i2cst->data, 0, sizeof(i2cst->data));
+
+    return;
+}
+
+/* Send data to TPM */
+static inline void tpm_tis_i2c_tpm_send(TPMStateI2C *i2cst)
+{
+    uint32_t data;
+
+    if ((i2cst->operation == OP_SEND) && (i2cst->offset > 1)) {
+
+        switch (i2cst->data[0]) {
+        case TPM_I2C_REG_DATA_CSUM_ENABLE:
+            /*
+             * Checksum is not handled by TIS code hence we will consume the
+             * register here.
+             */
+            i2cst->csum_enable = TPM_DATA_CSUM_ENABLED;
+            break;
+        case TPM_I2C_REG_DATA_FIFO:
+            /* Handled in the main i2c_send function */
+            break;
+        case TPM_I2C_REG_LOC_SEL:
+            /*
+             * This register is not handled by TIS so save the locality
+             * locally
+             */
+            i2cst->loc_sel = i2cst->data[1];
+            break;
+        default:
+            /* We handle non-FIFO here */
+
+            /* Index 0 is a register. Convert byte stream to uint32_t */
+            data = i2cst->data[1];
+            data |= i2cst->data[2] << 8;
+            data |= i2cst->data[3] << 16;
+            data |= i2cst->data[4] << 24;
+
+            /* Add register specific masking */
+            switch (i2cst->data[0]) {
+            case TPM_I2C_REG_INT_ENABLE:
+                data &= TPM_I2C_INT_ENABLE_MASK;
+                break;
+            }
+
+            tpm_tis_write_data(&i2cst->state, i2cst->tis_addr, data, 4);
+            break;
+        }
+
+        tpm_tis_i2c_clear_data(i2cst);
+    }
+
+    return;
+}
+
+/* Callback from TPM to indicate that response is copied */
+static void tpm_tis_i2c_request_completed(TPMIf *ti, int ret)
+{
+    TPMStateI2C *i2cst = TPM_TIS_I2C(ti);
+    TPMState *s = &i2cst->state;
+
+    /* Inform the common code. */
+    tpm_tis_request_completed(s, ret);
+}
+
+static enum TPMVersion tpm_tis_i2c_get_tpm_version(TPMIf *ti)
+{
+    TPMStateI2C *i2cst = TPM_TIS_I2C(ti);
+    TPMState *s = &i2cst->state;
+
+    return tpm_tis_get_tpm_version(s);
+}
+
+static int tpm_tis_i2c_event(I2CSlave *i2c, enum i2c_event event)
+{
+    TPMStateI2C *i2cst = TPM_TIS_I2C(i2c);
+    int ret = 0;
+
+    switch (event) {
+    case I2C_START_RECV:
+        trace_tpm_tis_i2c_event("START_RECV");
+        break;
+    case I2C_START_SEND:
+        trace_tpm_tis_i2c_event("START_SEND");
+        tpm_tis_i2c_clear_data(i2cst);
+        break;
+    case I2C_FINISH:
+        trace_tpm_tis_i2c_event("FINISH");
+        if (i2cst->operation == OP_SEND) {
+            tpm_tis_i2c_tpm_send(i2cst);
+        } else {
+            tpm_tis_i2c_clear_data(i2cst);
+        }
+        break;
+    default:
+        break;
+    }
+
+    return ret;
+}
+
+/*
+ * If data is for FIFO then it is received from tpm_tis_common buffer
+ * otherwise it will be handled using single call to common code and
+ * cached in the local buffer.
+ */
+static uint8_t tpm_tis_i2c_recv(I2CSlave *i2c)
+{
+    int          ret = 0;
+    uint32_t     data_read;
+    TPMStateI2C *i2cst = TPM_TIS_I2C(i2c);
+    TPMState    *s = &i2cst->state;
+    uint16_t     i2c_reg = i2cst->data[0];
+
+    if (i2cst->operation == OP_RECV) {
+
+        /* Do not cache FIFO data. */
+        if (i2cst->data[0] == TPM_I2C_REG_DATA_FIFO) {
+            data_read = tpm_tis_read_data(s, i2cst->tis_addr, 1);
+            ret = (data_read & 0xff);
+        } else if (i2cst->offset < sizeof(i2cst->data)) {
+            ret = i2cst->data[i2cst->offset++];
+        }
+
+    } else if ((i2cst->operation == OP_SEND) && (i2cst->offset < 2)) {
+        /* First receive call after send */
+
+        i2cst->operation = OP_RECV;
+
+        switch (i2c_reg) {
+        case TPM_I2C_REG_LOC_SEL:
+            /* Location selection register is managed by i2c */
+            i2cst->data[1] = i2cst->loc_sel;
+            break;
+        case TPM_I2C_REG_DATA_FIFO:
+            /* FIFO data is directly read from TPM TIS */
+            data_read = tpm_tis_read_data(s, i2cst->tis_addr, 1);
+            i2cst->data[1] = (data_read & 0xff);
+            break;
+        case TPM_I2C_REG_DATA_CSUM_ENABLE:
+            i2cst->data[1] = i2cst->csum_enable;
+            break;
+        case TPM_I2C_REG_INT_CAPABILITY:
+            /* Interrupt is not supported as there is not way to test it. */
+            i2cst->data[1] = TPM_I2C_INT_ENABLE_MASK;
+            i2cst->data[2] = TPM_I2C_INT_ENABLE_MASK;
+            i2cst->data[3] = TPM_I2C_INT_ENABLE_MASK;
+            i2cst->data[4] = TPM_I2C_INT_ENABLE_MASK;
+            break;
+        case TPM_I2C_REG_DATA_CSUM_GET:
+            /*
+             * Checksum registers are not supported by common code hence
+             * call a common code to get the checksum.
+             */
+            data_read = tpm_tis_get_checksum(s);
+
+            /* Save the byte stream in data field */
+            i2cst->data[1] = (data_read & 0xff);
+            i2cst->data[2] = ((data_read >> 8) & 0xff);
+            break;
+        default:
+            data_read = tpm_tis_read_data(s, i2cst->tis_addr, 4);
+
+            switch (i2c_reg) {
+            case TPM_I2C_REG_INTF_CAPABILITY:
+                /* Prepare the capabilities as per I2C interface */
+                data_read = tpm_i2c_interface_capability(i2cst,
+                                                         data_read);
+                break;
+            case TPM_I2C_REG_STS:
+                /*
+                 * As per specs, STS bit 31:26 are reserved and must
+                 * be set to 0
+                 */
+                data_read &= TPM_I2C_STS_READ_MASK;
+                break;
+            }
+
+            /* Save byte stream in data[] */
+            i2cst->data[1] = data_read;
+            i2cst->data[2] = data_read >> 8;
+            i2cst->data[3] = data_read >> 16;
+            i2cst->data[4] = data_read >> 24;
+            break;
+        }
+
+        /* Return first byte with this call */
+        i2cst->offset = 1; /* keep the register value intact for debug */
+        ret = i2cst->data[i2cst->offset++];
+    } else {
+        i2cst->operation = OP_RECV;
+    }
+
+    trace_tpm_tis_i2c_recv(ret);
+
+    return ret;
+}
+
+/*
+ * Send function only remembers data in the buffer and then calls
+ * TPM TIS common code during FINISH event.
+ */
+static int tpm_tis_i2c_send(I2CSlave *i2c, uint8_t data)
+{
+    TPMStateI2C *i2cst = TPM_TIS_I2C(i2c);
+
+    /* Reject non-supported registers. */
+    if (i2cst->offset == 0) {
+        /* Convert I2C register to TIS register */
+        tpm_tis_i2c_to_tis_reg(i2cst, data);
+        if (i2cst->tis_addr == 0xffffffff) {
+            return 0xffffffff;
+        }
+
+        trace_tpm_tis_i2c_send_reg(i2cst->reg_name, data);
+
+        /* We do not support device address change */
+        if (data == TPM_I2C_REG_I2C_DEV_ADDRESS) {
+            qemu_log_mask(LOG_UNIMP, "%s: Device address change "
+                          "is not supported.\n", __func__);
+            return 0xffffffff;
+        }
+    } else {
+        trace_tpm_tis_i2c_send(data);
+    }
+
+    if (i2cst->offset < sizeof(i2cst->data)) {
+        i2cst->operation = OP_SEND;
+
+        /* Remember data locally for non-FIFO registers */
+        if ((i2cst->offset == 0) ||
+            (i2cst->data[0] != TPM_I2C_REG_DATA_FIFO)) {
+            i2cst->data[i2cst->offset++] = data;
+        } else {
+            tpm_tis_write_data(&i2cst->state, i2cst->tis_addr, data, 1);
+        }
+
+        return 0;
+
+    }
+
+    /* Return non-zero to indicate NAK */
+    return 1;
+}
+
+static Property tpm_tis_i2c_properties[] = {
+    DEFINE_PROP_TPMBE("tpmdev", TPMStateI2C, state.be_driver),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void tpm_tis_i2c_realizefn(DeviceState *dev, Error **errp)
+{
+    TPMStateI2C *i2cst = TPM_TIS_I2C(dev);
+    TPMState *s = &i2cst->state;
+
+    if (!tpm_find()) {
+        error_setg(errp, "at most one TPM device is permitted");
+        return;
+    }
+
+    /*
+     * Get the backend pointer. It is not initialized propery during
+     * device_class_set_props
+     */
+    s->be_driver = qemu_find_tpm_be("tpm0");
+
+    if (!s->be_driver) {
+        error_setg(errp, "'tpmdev' property is required");
+        return;
+    }
+}
+
+static void tpm_tis_i2c_reset(DeviceState *dev)
+{
+    TPMStateI2C *i2cst = TPM_TIS_I2C(dev);
+    TPMState *s = &i2cst->state;
+
+    tpm_tis_i2c_clear_data(i2cst);
+
+    i2cst->csum_enable = 0;
+    i2cst->loc_sel = 0x00;
+
+    return tpm_tis_reset(s);
+}
+
+static void tpm_tis_i2c_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    I2CSlaveClass *k = I2C_SLAVE_CLASS(klass);
+    TPMIfClass *tc = TPM_IF_CLASS(klass);
+
+    dc->realize = tpm_tis_i2c_realizefn;
+    dc->reset = tpm_tis_i2c_reset;
+    dc->vmsd = &vmstate_tpm_tis_i2c;
+    device_class_set_props(dc, tpm_tis_i2c_properties);
+    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
+
+    k->event = tpm_tis_i2c_event;
+    k->recv = tpm_tis_i2c_recv;
+    k->send = tpm_tis_i2c_send;
+
+    tc->model = TPM_MODEL_TPM_TIS;
+    tc->request_completed = tpm_tis_i2c_request_completed;
+    tc->get_version = tpm_tis_i2c_get_tpm_version;
+}
+
+static const TypeInfo tpm_tis_i2c_info = {
+    .name          = TYPE_TPM_TIS_I2C,
+    .parent        = TYPE_I2C_SLAVE,
+    .instance_size = sizeof(TPMStateI2C),
+    .class_init    = tpm_tis_i2c_class_init,
+        .interfaces = (InterfaceInfo[]) {
+        { TYPE_TPM_IF },
+        { }
+    }
+};
+
+static void tpm_tis_i2c_register_types(void)
+{
+    type_register_static(&tpm_tis_i2c_info);
+}
+
+type_init(tpm_tis_i2c_register_types)
diff --git a/hw/tpm/trace-events b/hw/tpm/trace-events
index f17110458e..fa882dfefe 100644
--- a/hw/tpm/trace-events
+++ b/hw/tpm/trace-events
@@ -36,3 +36,9 @@ tpm_spapr_do_crq_unknown_msg_type(uint8_t type) "Unknown message 
type 0x%02x"
  tpm_spapr_do_crq_unknown_crq(uint8_t raw1, uint8_t raw2) "unknown CRQ 0x%02x 
0x%02x ..."
  tpm_spapr_post_load(void) "Delivering TPM response after resume"
  tpm_spapr_caught_response(uint32_t v) "Caught response to deliver after resume: %u 
bytes"
+
+# tpm_tis_i2c.c
+tpm_tis_i2c_recv(uint8_t data) "TPM I2C read: 0x%X"
+tpm_tis_i2c_send(uint8_t data) "TPM I2C write: 0x%X"
+tpm_tis_i2c_event(const char *event) "TPM I2C event: %s"
+tpm_tis_i2c_send_reg(const char *name, int reg) "TPM I2C write register: 
%s(0x%X)"
diff --git a/include/sysemu/tpm.h b/include/sysemu/tpm.h
index fb40e30ff6..66e3b45f30 100644
--- a/include/sysemu/tpm.h
+++ b/include/sysemu/tpm.h
@@ -48,6 +48,7 @@ struct TPMIfClass {
  #define TYPE_TPM_TIS_SYSBUS         "tpm-tis-device"
  #define TYPE_TPM_CRB                "tpm-crb"
  #define TYPE_TPM_SPAPR              "tpm-spapr"
+#define TYPE_TPM_TIS_I2C            "tpm-tis-i2c"
#define TPM_IS_TIS_ISA(chr) \
      object_dynamic_cast(OBJECT(chr), TYPE_TPM_TIS_ISA)
@@ -57,6 +58,8 @@ struct TPMIfClass {
      object_dynamic_cast(OBJECT(chr), TYPE_TPM_CRB)
  #define TPM_IS_SPAPR(chr)                           \
      object_dynamic_cast(OBJECT(chr), TYPE_TPM_SPAPR)
+#define TPM_IS_TIS_I2C(chr)                      \
+    object_dynamic_cast(OBJECT(chr), TYPE_TPM_TIS_I2C)
/* returns NULL unless there is exactly one TPM device */
  static inline TPMIf *tpm_find(void)




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