linux-kernel - Re: [PATCH V2] firmware: qcom_scm: use the SCM

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Date:   Fri, 15 Sep 2023 08:21:43 -0700
From:   Bjorn Andersson <andersson@...nel.org>
To:     Kathiravan T <quic_kathirav@...cinc.com>,
        Elliot Berman <quic_eberman@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_eberman@...cinc.com, stable@...r.kernel.org
Subject: Re: [PATCH V2] firmware: qcom_scm: use the SCM_CONVENTION based on
 ARM / ARM64

On Wed, Jun 07, 2023 at 10:23:45AM +0530, Kathiravan T 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.
> 
> To avoid this, use SMC_CONVENTION_ARM_64 only on ARM64 builds.
> 

My memory of this is cloudy, but I feel the logic is complicated because
early 64-bit boards all used 32-bit TZ. So, I really would like Elliot's
input before picking this change.

Regards,
Bjorn

> Cc: stable@...r.kernel.org
> Fixes: 9a434cee773a ("firmware: qcom_scm: Dynamically support SMCCC and legacy conventions")
> Signed-off-by: Kathiravan T <quic_kathirav@...cinc.com>
> ---
> Changes in V2:
> 	- Added the Fixes tag and cc'd stable mailing list
> 
>  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
>  
>  	probed_convention = SMC_CONVENTION_ARM_32;
>  	ret = __scm_smc_call(NULL, &desc, probed_convention, &res, true);
> -- 
> 2.17.1
>