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

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Date:   Fri, 15 Sep 2023 22:10:32 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bjorn Andersson <andersson@...nel.org>
Cc:     Kathiravan T <quic_kathirav@...cinc.com>,
        Elliot Berman <quic_eberman@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH V2] firmware: qcom_scm: use the SCM_CONVENTION based on
 ARM / ARM64

On Fri, 15 Sept 2023 at 18:17, Bjorn Andersson <andersson@...nel.org> wrote:
>
> 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.

But this codepath is not changed by this patch. Only the 32-bit
codepath is altered.

>
> 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
> >



-- 
With best wishes
Dmitry