Re: [PATCH] fsl-imx: Add simple RTC emulation for i.MX6 and i.MX7 boards

[Peter Maydell]

On Sun, 12 Nov 2023 at 09:22, Nikita Ostrenkov <n.ostrenkov@gmail.com> wrote:

Hi; thanks for this patch, and sorry I haven't got round
to reviewing it earlier.

> Signed-off-by: Nikita Ostrenkov <n.ostrenkov@gmail.com>
> ---
>  hw/misc/imx7_snvs.c         | 59 ++++++++++++++++++++++++++++++++-----
>  hw/misc/trace-events        |  4 +--
>  include/hw/misc/imx7_snvs.h | 14 ++++++++-
>  3 files changed, 67 insertions(+), 10 deletions(-)
>
> diff --git a/hw/misc/imx7_snvs.c b/hw/misc/imx7_snvs.c
> index a245f96cd4..7ef3e4901a 100644
> --- a/hw/misc/imx7_snvs.c
> +++ b/hw/misc/imx7_snvs.c
> @@ -13,29 +13,74 @@
>   */
>
>  #include "qemu/osdep.h"
> +#include "qemu/timer.h"
>  #include "hw/misc/imx7_snvs.h"
>  #include "qemu/module.h"
> +#include "sysemu/sysemu.h"
>  #include "sysemu/runstate.h"
>  #include "trace.h"
>
> +#define RTC_FREQ    32768ULL
> +
> +static uint64_t imx7_snvs_get_count(IMX7SNVSState *s)
> +{
> +    int64_t now_ms = qemu_clock_get_ns(rtc_clock) / 1000000;
> +    return s->tick_offset + now_ms * RTC_FREQ / 1000;

This kind of clock-to-ticks calculation should generally
be done with muldiv64() to avoid possible overflows:

    int64_t ticks = muldiv64(qemu_clock_get_ns(rtc_clock), RTC_FREQ,
NANOSECONDS_PER_SECOND);
    return s->tick_offset + ticks;

> +}
> +
>  static uint64_t imx7_snvs_read(void *opaque, hwaddr offset, unsigned size)
>  {
> -    trace_imx7_snvs_read(offset, 0);
> +    IMX7SNVSState *s = opaque;
> +    uint64_t ret = 0;
> +
> +    switch (offset) {
> +    case SNVS_LPSRTCMR:
> +        ret = (imx7_snvs_get_count(s) >> 32) & 0x7fffU;
> +        break;
> +    case SNVS_LPSRTCLR:
> +        ret = imx7_snvs_get_count(s) & 0xffffffffU;
> +        break;
> +    case SNVS_LPCR:
> +        ret = s->lpcr;
> +        break;
> +    }
> +
> +    trace_imx7_snvs_read(offset, ret, size);
>
> -    return 0;
> +    return ret;
>  }
>
>  static void imx7_snvs_write(void *opaque, hwaddr offset,
>                              uint64_t v, unsigned size)
>  {
> -    const uint32_t value = v;
> -    const uint32_t mask  = SNVS_LPCR_TOP | SNVS_LPCR_DP_EN;
> +    trace_imx7_snvs_write(offset, v, size);
>
> -    trace_imx7_snvs_write(offset, value);
> +    IMX7SNVSState *s = opaque;
>
> -    if (offset == SNVS_LPCR && ((value & mask) == mask)) {
> -        qemu_system_shutdown_request(SHUTDOWN_CAUSE_GUEST_SHUTDOWN);
> +    uint64_t new_value = 0;
> +
> +    switch (offset) {
> +    case SNVS_LPSRTCMR:
> +        new_value = (imx7_snvs_get_count(s) & 0xffffffffU) | (v << 32);
> +        break;
> +    case SNVS_LPSRTCLR:
> +        new_value = (imx7_snvs_get_count(s) & 0x7fff00000000ULL) | v;
> +        break;
> +    case SNVS_LPCR: {
> +        s->lpcr = v;
> +
> +        const uint32_t value = v;
> +        const uint32_t mask  = SNVS_LPCR_TOP | SNVS_LPCR_DP_EN;
> +
> +        if ((value & mask) == mask)
> +            qemu_system_shutdown_request(SHUTDOWN_CAUSE_GUEST_SHUTDOWN);
> +
> +        break;
> +    }
>      }
> +
> +    if (offset == SNVS_LPSRTCMR || offset == SNVS_LPSRTCLR)
> +        s->tick_offset += new_value - imx7_snvs_get_count(s);

Our coding standard requires braces on all if() statements,
even single line ones.

I think for this update-the-count handling we should call
imx7_snvs_get_count() only once, and then use that value
both in constructing new_value and also here where we
calculate the tick_offset.

>  }

I think you need to initialise s->tick_offset in the
device init routine, similar to what the pl031 device does.

>  static const struct MemoryRegionOps imx7_snvs_ops = {
> diff --git a/hw/misc/trace-events b/hw/misc/trace-events
> index 05ff692441..85725506bf 100644
> --- a/hw/misc/trace-events
> +++ b/hw/misc/trace-events
> @@ -116,8 +116,8 @@ imx7_gpr_read(uint64_t offset) "addr 0x%08" PRIx64
>  imx7_gpr_write(uint64_t offset, uint64_t value) "addr 0x%08" PRIx64 "value 
> 0x%08" PRIx64
>
>  # imx7_snvs.c
> -imx7_snvs_read(uint64_t offset, uint32_t value) "addr 0x%08" PRIx64 "value 
> 0x%08" PRIx32
> -imx7_snvs_write(uint64_t offset, uint32_t value) "addr 0x%08" PRIx64 "value 
> 0x%08" PRIx32
> +imx7_snvs_read(uint64_t offset, uint64_t value, unsigned size) "i.MX SNVS 
> read: offset 0x%08" PRIx64 " value 0x%08" PRIx64 " size %u"
> +imx7_snvs_write(uint64_t offset, uint64_t value, unsigned size) "i.MX SNVS 
> write: offset 0x%08" PRIx64 " value 0x%08" PRIx64 " size %u"
>
>  # mos6522.c
>  mos6522_set_counter(int index, unsigned int val) "T%d.counter=%d"
> diff --git a/include/hw/misc/imx7_snvs.h b/include/hw/misc/imx7_snvs.h
> index 14a1d6fe6b..406c1fe97f 100644
> --- a/include/hw/misc/imx7_snvs.h
> +++ b/include/hw/misc/imx7_snvs.h
> @@ -20,7 +20,9 @@
>  enum IMX7SNVSRegisters {
>      SNVS_LPCR = 0x38,
>      SNVS_LPCR_TOP   = BIT(6),
> -    SNVS_LPCR_DP_EN = BIT(5)
> +    SNVS_LPCR_DP_EN = BIT(5),
> +    SNVS_LPSRTCMR = 0x050, /* Secure Real Time Counter MSB Register */
> +    SNVS_LPSRTCLR = 0x054, /* Secure Real Time Counter LSB Register */
>  };
>
>  #define TYPE_IMX7_SNVS "imx7.snvs"
> @@ -31,6 +33,16 @@ struct IMX7SNVSState {
>      SysBusDevice parent_obj;
>
>      MemoryRegion mmio;
> +
> +    /*
> +     * Needed to preserve the tick_count across migration, even if the
> +     * absolute value of the rtc_clock is different on the source and
> +     * destination.
> +     */
> +    int64_t tick_offset_vmstate;

You don't need tick_offset_vmstate -- it is only in the p031
RTC device as a backwards-compatibility thing for older versions
of QEMU. Migrating tick_offset alone is sufficient in a new
device. (It seems to have been unfortunately copied-and-pasted
into the goldfish RTC device; we should probably fix that bug.)

> +    int64_t tick_offset;
> +
> +    uint64_t lpcr;

We've now added state to this device, which means that it needs
a VMState structure to handle migration, and it needs a reset
function.

>  };
>
>  #endif /* IMX7_SNVS_H */
> --

thanks
-- PMM