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Re: [Qemu-ppc] [PATCH v2 3/8] ppc4xx_i2c: Implement directcntl register


From: BALATON Zoltan
Subject: Re: [Qemu-ppc] [PATCH v2 3/8] ppc4xx_i2c: Implement directcntl register
Date: Wed, 13 Jun 2018 16:03:18 +0200 (CEST)
User-agent: Alpine 2.21 (BSF 202 2017-01-01)

On Wed, 13 Jun 2018, David Gibson wrote:
On Wed, Jun 13, 2018 at 10:54:22AM +0200, BALATON Zoltan wrote:
On Wed, 13 Jun 2018, David Gibson wrote:
On Wed, Jun 06, 2018 at 03:31:48PM +0200, BALATON Zoltan wrote:
Signed-off-by: BALATON Zoltan <address@hidden>
---
 default-configs/ppc-softmmu.mak    |  1 +
 default-configs/ppcemb-softmmu.mak |  1 +
 hw/i2c/ppc4xx_i2c.c                | 14 +++++++++++++-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/default-configs/ppc-softmmu.mak b/default-configs/ppc-softmmu.mak
index 4d7be45..7d0dc2f 100644
--- a/default-configs/ppc-softmmu.mak
+++ b/default-configs/ppc-softmmu.mak
@@ -26,6 +26,7 @@ CONFIG_USB_EHCI_SYSBUS=y
 CONFIG_SM501=y
 CONFIG_IDE_SII3112=y
 CONFIG_I2C=y
+CONFIG_BITBANG_I2C=y

 # For Macs
 CONFIG_MAC=y
diff --git a/default-configs/ppcemb-softmmu.mak 
b/default-configs/ppcemb-softmmu.mak
index 67d18b2..37af193 100644
--- a/default-configs/ppcemb-softmmu.mak
+++ b/default-configs/ppcemb-softmmu.mak
@@ -19,3 +19,4 @@ CONFIG_USB_EHCI_SYSBUS=y
 CONFIG_SM501=y
 CONFIG_IDE_SII3112=y
 CONFIG_I2C=y
+CONFIG_BITBANG_I2C=y
diff --git a/hw/i2c/ppc4xx_i2c.c b/hw/i2c/ppc4xx_i2c.c
index a68b5f7..5806209 100644
--- a/hw/i2c/ppc4xx_i2c.c
+++ b/hw/i2c/ppc4xx_i2c.c
@@ -30,6 +30,7 @@
 #include "cpu.h"
 #include "hw/hw.h"
 #include "hw/i2c/ppc4xx_i2c.h"
+#include "bitbang_i2c.h"

 #define PPC4xx_I2C_MEM_SIZE 18

@@ -46,7 +47,13 @@

 #define IIC_XTCNTLSS_SRST   (1 << 0)

+#define IIC_DIRECTCNTL_SDAC (1 << 3)
+#define IIC_DIRECTCNTL_SCLC (1 << 2)
+#define IIC_DIRECTCNTL_MSDA (1 << 1)
+#define IIC_DIRECTCNTL_MSCL (1 << 0)
+
 typedef struct {
+    bitbang_i2c_interface *bitbang;
     uint8_t mdata;
     uint8_t lmadr;
     uint8_t hmadr;
@@ -308,7 +315,11 @@ static void ppc4xx_i2c_writeb(void *opaque, hwaddr addr, 
uint64_t value,
         i2c->xtcntlss = value;
         break;
     case 16:
-        i2c->directcntl = value & 0x7;
+        i2c->directcntl = value & (IIC_DIRECTCNTL_SDAC & IIC_DIRECTCNTL_SCLC);
+        i2c->directcntl |= (value & IIC_DIRECTCNTL_SCLC ? 1 : 0);
+        bitbang_i2c_set(i2c->bitbang, BITBANG_I2C_SCL, i2c->directcntl & 1);

Shouldn't that use i2c->directcntl & IIC_DIRECTCNTL_MSCL ?

+        i2c->directcntl |= bitbang_i2c_set(i2c->bitbang, BITBANG_I2C_SDA,
+                               (value & IIC_DIRECTCNTL_SDAC) != 0) << 1;

Last expression might be clearer as:
        value & IIC_DIRECTCNTL_SDAC ? IIC_DIRECTCNTL_MSDA : 0

I guess this is a matter of taste but to me IIC_DIRECTCNTL_MSDA is a bit
position in the register so I use that when accessing that bit but when I
check for the values of a bit being 0 or 1 I don't use the define which is
for something else, just happens to have value 1 as well.

Hmm.. but the bit is being store in i2c->directcntl, which means it
can be read back from the register in that position, no?

Which of the above two do you mean?

In the first one I test for the 1/0 value set by the previous line before the bitbang_i2c_set call. This could be accessed as MSCL later but using that here would just make it longer and less obvious. If I want to be absolutely precise maybe it should be (value & IIC_DIRECTCNTL_SCL ? 1 : 0) in this line too but that was just stored in the register one line before so I can reuse that here as well. Otherwise I could add another variable just for this bit value and use that in both lines but why make it more complicated for a simple 1 or 0 value?

In the second case using MSDA is really not correct because the level to set is defined by SDAC bit. The SDAC, SCLC bits are what the program sets to tell which states the two i2c lines should be and the MSDA, MSCL are read only bits that show what states the lines really are.

IIC_DIRECTCNTL_MSDA has value of 1 but it means the second bit in the directcntl reg (which could have 0 or 1 value) not 1 value of a bit or i2c line.

Regards,
BALATON Zoltan



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