linux-kernel - Re: [PATCH 0/3] iommu/arm-smmu: Qualcomm bootsplash/efifb

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Date:   Mon, 24 May 2021 22:28:10 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu@...ts.linux-foundation.org,
        open list <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Patrick Daly <pdaly@...eaurora.org>,
        Pratik Patel <pratikp@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        Thierry Reding <treding@...dia.com>
Subject: Re: [PATCH 0/3] iommu/arm-smmu: Qualcomm bootsplash/efifb

On Mon 24 May 07:03 CDT 2021, Lee Jones wrote:

> On Wed, 8 Jan 2020 at 09:16, Will Deacon <will@...nel.org> wrote:
> 
> > On Thu, Dec 26, 2019 at 02:17:06PM -0800, Bjorn Andersson wrote:
> > > These patches implements the stream mapping inheritance that's necessary
> > in
> > > order to not hit a security violation as the display hardware looses its
> > stream
> > > mapping during initialization of arm-smmu in various Qualcomm platforms.
> > >
> > > This was previously posted as an RFC [1], changes since then involves the
> > > rebase and migration of the read-back code to the Qualcomm specific
> > > implementation, the mapping is maintained indefinitely - to handle probe
> > > deferring clients - and rewritten commit messages.
> >
> > I don't think we should solve this in a Qualcomm-specific manner. Please
> > can
> > you take a look at the proposal from Thierry [1] and see whether or not it
> > works for you?
> >
> 
> Did this or Thierry's solution ever gain traction?
> 

There was a few pieces that landed in the common code which allowed us
to deal with the quirks of the Qualcomm platform (turned out that just
reading back the settings wasn't the only piece necessary).

The "generic" solution is essentially the second half of
qcom_smmu_cfg_probe(), which ensures that as the SMMU is reset it will
do so with bypass mappings for all stream mappings the boot loader left
us.

> Or are all the parties still 'solving' this downstream?
> 

I believe that Qualcomm has adopted the upstream solution in their
downstream kernel.

Regards,
Bjorn