linux-kernel - Re: [PATCH] iommu: io-pgtable: Support non-coherent page tables

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Message-ID: <20190624115349.f62uqypyt7l73skf@willie-the-truck>
Date:   Mon, 24 Jun 2019 12:53:49 +0100
From:   Will Deacon <will@...nel.org>
To:     Will Deacon <will.deacon@....com>, bjorn.andersson@...aro.org
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Vivek Gautam <vgautam@....qualcomm.com>
Subject: Re: [PATCH] iommu: io-pgtable: Support non-coherent page tables

Hi again, Bjorn,

On Tue, Jun 18, 2019 at 06:39:33PM +0100, Will Deacon wrote:
> On Wed, May 15, 2019 at 04:32:34PM -0700, Bjorn Andersson wrote:
> > Describe the memory related to page table walks as non-cachable for iommu
> > instances that are not DMA coherent.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> >  drivers/iommu/io-pgtable-arm.c | 12 +++++++++---
> >  1 file changed, 9 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> > index 4e21efbc4459..68ff22ffd2cb 100644
> > --- a/drivers/iommu/io-pgtable-arm.c
> > +++ b/drivers/iommu/io-pgtable-arm.c
> > @@ -803,9 +803,15 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
> >  		return NULL;
> >  
> >  	/* TCR */
> > -	reg = (ARM_LPAE_TCR_SH_IS << ARM_LPAE_TCR_SH0_SHIFT) |
> > -	      (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_IRGN0_SHIFT) |
> > -	      (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_ORGN0_SHIFT);
> > +	if (cfg->quirks & IO_PGTABLE_QUIRK_NO_DMA) {
> > +		reg = (ARM_LPAE_TCR_SH_IS << ARM_LPAE_TCR_SH0_SHIFT) |
> > +		      (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_IRGN0_SHIFT) |
> > +		      (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_ORGN0_SHIFT);
> > +	} else {
> > +		reg = (ARM_LPAE_TCR_SH_IS << ARM_LPAE_TCR_SH0_SHIFT) |
> 
> Nit: this should be outer-shareable (ARM_LPAE_TCR_SH_OS).
> 
> > +		      (ARM_LPAE_TCR_RGN_NC << ARM_LPAE_TCR_IRGN0_SHIFT) |
> > +		      (ARM_LPAE_TCR_RGN_NC << ARM_LPAE_TCR_ORGN0_SHIFT);
> > +	}
> 
> Should we also be doing something similar for the short-descriptor code
> in io-pgtable-arm-v7s.c? Looks like you just need to use ARM_V7S_RGN_NC
> instead of ARM_V7S_RGN_WBWA when initialising ttbr0 for non-coherent
> SMMUs.

Do you plan to respin this? I'll need it this week if you're shooting for
5.3.

Thanks,

Will