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

From: Rob Clark <robdclark@gmail.com>
To: Will Deacon <will@kernel.org>
Cc: freedreno <freedreno@lists.freedesktop.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,
	" <iommu@lists.linux-foundation.org>,
	John Stultz <john.stultz@linaro.org>,
	Robin Murphy <robin.murphy@arm.com>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [Freedreno] [PATCH v9 4/7] iommu/arm-smmu: Add a pointer to the attached device to smmu_domain
Date: Thu, 16 Jul 2020 07:10:43 -0700	[thread overview]
Message-ID: <CAF6AEGtf2Ts5_S-3DDA0i_ega-MjJK5tyy=peW6ar0c1ZD72Rw@mail.gmail.com> (raw)
In-Reply-To: <20200716085053.GB6771@willie-the-truck>

On Thu, Jul 16, 2020 at 1:51 AM Will Deacon <will@kernel.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
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