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

[Kathiravan T <quic_kathirav@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?


Ack. Will add it in next spin.


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


You want to remove the of_device_is_compatible check and by default set 
the 'forced' to true, if the SCM call fails? Currently it clearly states 
why we are forcing the convention. If we remove it, we may not able to 
identify which target FW lacks this scm call support and why we are 
forcing it...


Thanks,

>
> Thanks,
> Bhupesh