linux-kernel - Re: [PATCHv7 1/7] iommu/io-pgtable-arm: Add support to use system cache

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Message-ID: <20201112094353.GB19049@willie-the-truck>
Date:   Thu, 12 Nov 2020 09:43:53 +0000
From:   Will Deacon <will@...nel.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        freedreno@...ts.freedesktop.org,
        "Kristian H . Kristensen" <hoegsberg@...gle.com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCHv7 1/7] iommu/io-pgtable-arm: Add support to use system
 cache

On Wed, Nov 11, 2020 at 11:32:42AM +0530, Sai Prakash Ranjan wrote:
> On 2020-11-10 17:48, Will Deacon wrote:
> > On Fri, Oct 30, 2020 at 02:53:08PM +0530, Sai Prakash Ranjan wrote:
> > > Add a quirk IO_PGTABLE_QUIRK_SYS_CACHE to override the
> > > attributes set in TCR for the page table walker when
> > > using system cache.
> > > 
> > > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> > > ---
> > >  drivers/iommu/io-pgtable-arm.c | 7 ++++++-
> > >  include/linux/io-pgtable.h     | 4 ++++
> > >  2 files changed, 10 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/iommu/io-pgtable-arm.c
> > > b/drivers/iommu/io-pgtable-arm.c
> > > index a7a9bc08dcd1..a356caf1683a 100644
> > > --- a/drivers/iommu/io-pgtable-arm.c
> > > +++ b/drivers/iommu/io-pgtable-arm.c
> > > @@ -761,7 +761,8 @@ arm_64_lpae_alloc_pgtable_s1(struct
> > > io_pgtable_cfg *cfg, void *cookie)
> > > 
> > >  	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
> > >  			    IO_PGTABLE_QUIRK_NON_STRICT |
> > > -			    IO_PGTABLE_QUIRK_ARM_TTBR1))
> > > +			    IO_PGTABLE_QUIRK_ARM_TTBR1 |
> > > +			    IO_PGTABLE_QUIRK_SYS_CACHE))
> > >  		return NULL;
> > > 
> > >  	data = arm_lpae_alloc_pgtable(cfg);
> > > @@ -773,6 +774,10 @@ arm_64_lpae_alloc_pgtable_s1(struct
> > > io_pgtable_cfg *cfg, void *cookie)
> > >  		tcr->sh = ARM_LPAE_TCR_SH_IS;
> > >  		tcr->irgn = ARM_LPAE_TCR_RGN_WBWA;
> > >  		tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;
> > > +	} else if (cfg->quirks & IO_PGTABLE_QUIRK_SYS_CACHE) {
> > > +		tcr->sh = ARM_LPAE_TCR_SH_OS;
> > > +		tcr->irgn = ARM_LPAE_TCR_RGN_NC;
> > > +		tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;
> > 
> > Given that this only applies in the case where then page-table walker is
> > non-coherent, I think we'd be better off renaming the quirk to something
> > like IO_PGTABLE_QUIRK_ARM_OUTER_WBWA and then rejecting it in the
> > non-coherent case.
> > 
> 
> Do you mean like below?
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index a7a9bc08dcd1..94de1f71db42 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -776,7 +776,10 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg
> *cfg, void *cookie)
>         } else {
>                 tcr->sh = ARM_LPAE_TCR_SH_OS;
>                 tcr->irgn = ARM_LPAE_TCR_RGN_NC;
> -               tcr->orgn = ARM_LPAE_TCR_RGN_NC;
> +               if (!(cfg->quirks & IO_PGTABLE_QUIRK_ARM_OUTER_WBWA))
> +                       tcr->orgn = ARM_LPAE_TCR_RGN_NC;
> +               else
> +                       tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;

Yes, but rejecting the quirk if the walker is coherent (I accidentally said
"non-coherent" earlier on).

Will