Re: [PATCH] firmware: qcom_scm: use the SCM_CONVENTION based on ARM / ARM64

[Mukesh Ojha <quic_mojha@quicinc.com>]

On 5/22/2023 12:03 PM, Bhupesh Sharma wrote:
> Hi,
> 
> On Mon, 22 May 2023 at 10:15, Kathiravan T <quic_kathirav@quicinc.com> wrote:
>>
>> During SCM probe, to identify the SCM convention, scm call is made with
>> SMC_CONVENTION_ARM_64 followed by SMC_CONVENTION_ARM_32. Based on the
>> result what convention to be used is decided.
>>
>> IPQ chipsets starting from IPQ807x, supports both 32bit and 64bit kernel
>> variants, however TZ firmware runs in 64bit mode. When running on 32bit
>> kernel, scm call is made with SMC_CONVENTION_ARM_64 is causing the
>> system crash, due to the difference in the register sets between ARM and
>> AARCH64, which is accessed by the TZ.
> 
> If a crash is being fixed, should we use a Fixes tag as well?
> 
>> To avoid this, use SMC_CONVENTION_ARM_64 only on ARM64 builds.
>>
>> Signed-off-by: Kathiravan T <quic_kathirav@quicinc.com>
>> ---
>>   drivers/firmware/qcom_scm.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
>> index fde33acd46b7..db6754db48a0 100644
>> --- a/drivers/firmware/qcom_scm.c
>> +++ b/drivers/firmware/qcom_scm.c
>> @@ -171,6 +171,7 @@ static enum qcom_scm_convention __get_convention(void)
>>          if (likely(qcom_scm_convention != SMC_CONVENTION_UNKNOWN))
>>                  return qcom_scm_convention;
>>
>> +#if IS_ENABLED(CONFIG_ARM64)
>>          /*
>>           * Device isn't required as there is only one argument - no device
>>           * needed to dma_map_single to secure world
>> @@ -191,6 +192,7 @@ static enum qcom_scm_convention __get_convention(void)
>>                  forced = true;
>>                  goto found;
>>          }
>> +#endif
> 
> If we are already inside a 'CONFIG_ARM64' define here ^^^, do we even
> need the following snippet now:
> 
> /*
>       * Some SC7180 firmwares didn't implement the
>       * QCOM_SCM_INFO_IS_CALL_AVAIL call, so we fallback to forcing ARM_64
>       * calling conventions on these firmwares. Luckily we don't make any
>       * early calls into the firmware on these SoCs so the device pointer
>       * will be valid here to check if the compatible matches.
>       */
>      if (of_device_is_compatible(__scm ? __scm->dev->of_node : NULL,
> "qcom,scm-sc7180")) {
>          forced = true;
>          goto found;
>      }
> 
> 'forced' will always be 'true' now that we are inside the CONFIG_ARM64
> check above, right?

Well, i think you can't get rid off the variable here as main purpose
of the variable seems to be print the mode is being forced here
(kind of workaround for a firmware) here and not natural.

is not that ?

-- Mukesh

> So, maybe you can clean-up that path as well.
> 
> Thanks,
> Bhupesh