linux-kernel - Re: [Freedreno] [PATCH v9 4/7] iommu/arm-smmu: Add a pointer to the attached device to smmu_domain

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Date:   Thu, 16 Jul 2020 07:10:43 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Will Deacon <will@...nel.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        John Stultz <john.stultz@...aro.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Freedreno] [PATCH v9 4/7] iommu/arm-smmu: Add a pointer to the
 attached device to smmu_domain

On Thu, Jul 16, 2020 at 1:51 AM Will Deacon <will@...nel.org> wrote:
>
> On Mon, Jul 13, 2020 at 11:19:17AM -0600, Jordan Crouse wrote:
> > On Mon, Jul 13, 2020 at 04:09:02PM +0100, Will Deacon wrote:
> > > On Fri, Jun 26, 2020 at 02:00:38PM -0600, Jordan Crouse wrote:
> > > > diff --git a/drivers/iommu/arm-smmu.h b/drivers/iommu/arm-smmu.h
> > > > index 5f2de20e883b..d33cfe26b2f5 100644
> > > > --- a/drivers/iommu/arm-smmu.h
> > > > +++ b/drivers/iommu/arm-smmu.h
> > > > @@ -345,6 +345,7 @@ struct arm_smmu_domain {
> > > >   struct mutex                    init_mutex; /* Protects smmu pointer */
> > > >   spinlock_t                      cb_lock; /* Serialises ATS1* ops and TLB syncs */
> > > >   struct iommu_domain             domain;
> > > > + struct device                   *dev;   /* Device attached to this domain */
> > >
> > > This really doesn't feel right to me -- you can generally have multiple
> > > devices attached to a domain and they can come and go without the domain
> > > being destroyed. Perhaps you could instead identify the GPU during
> > > cfg_probe() and squirrel that information away somewhere?
> >
> > I need some help here. The SMMU device (qcom,adreno-smmu) will have at least two
> > stream ids from two different platform devices (GPU and GMU) and I need to
> > configure split-pagetable and stall/terminate differently on the two domains.
>
> Hmm. How does the GPU driver know which context bank is assigned to the GPU
> and which one is assigned to the GMU? I assume it needs this information so
> that it can play its nasty tricks with the TTBR registers?
>
> I ask because if we need to guarantee stability of the context-bank
> assignment, then you could match on that in the ->init_context() callback,
> but now I worry that it currently works by luck :/

Yeah, it is basically by luck right now.. some sort of impl callback
which was passed the dev into impl->init_context() might do the trick
(ie. then the impl could match on compat string)

BR,
-R

> Do we need to add an extra callback to allocate the context bank?
>
> Will
> _______________________________________________
> Freedreno mailing list
> Freedreno@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/freedreno

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