linux-kernel - Re: [PATCH v2 05/11] clk: qcom: gcc-msm8998: Mark gpu_cfg_ahb

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Date:   Thu, 14 Jan 2021 17:09:41 -0700
From:   Jeffrey Hugo <jeffrey.l.hugo@...il.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Cc:     MSM <linux-arm-msm@...r.kernel.org>, konrad.dybcio@...ainline.org,
        marijn.suijten@...ainline.org, martin.botka@...ainline.org,
        phone-devel@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, linux-clk@...r.kernel.org,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 05/11] clk: qcom: gcc-msm8998: Mark gpu_cfg_ahb_clk as critical

On Thu, Jan 14, 2021 at 4:05 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@...ainline.org> wrote:
>
> Il 14/01/21 23:37, Jeffrey Hugo ha scritto:
> > On Thu, Jan 14, 2021 at 3:13 PM AngeloGioacchino Del Regno
> > <angelogioacchino.delregno@...ainline.org> wrote:
> >>
> >> The GPU IOMMU depends on this clock and the hypervisor will crash
> >> the SoC if this clock gets disabled because the secure contexts
> >> that have been set on this IOMMU by the bootloader will become
> >> unaccessible (or they get reset).
> >> Mark this clock as critical to avoid this issue when the Adreno
> >> GPU is enabled.
> >>
> >
> > You should go review the last attempt to do this -
> > https://lkml.org/lkml/2019/12/17/881
> >
>
> Thanks for the tip, but unfortunately this isn't possible on the
> gpu_cfg_ahb_clk, as it is also needed for the Adreno IOMMU, which has
> secure contexts that are set up from one of the bootloader stages and if
> you reset/"mess up" one of them (by - in this case - un-clocking the
> MMU), then the hypervisor will kick in and generate a fault, rebooting
> the SoC.
>
> Of course, this scenario is for the case in which you want to boot the
> device without any gpucc nor any runtime pm user of that.. and the
> aforementioned issue makes that solution not really usable.
>
> Again, unfortunately.

Intresting, that's not true on all devices, but presumably you have
devices where it is.  Fun.