linux-kernel - Re: [PATCH v3 4/5] iommu/io-pgtable-dart: Add DART PTE support for t6000

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Date:   Thu, 1 Sep 2022 02:22:34 +0200
From:   Janne Grunau <j@...nau.net>
To:     Robin Murphy <robin.murphy@....com>
Cc:     iommu@...ts.linux-foundation.org,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        asahi@...ts.linux.dev, Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Georgi Djakov <quic_c_gdjako@...cinc.com>,
        Hector Martin <marcan@...can.st>,
        "Isaac J. Manjarres" <isaacm@...eaurora.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/5] iommu/io-pgtable-dart: Add DART PTE support for
 t6000

On 2022-06-27 16:13:20 +0100, Robin Murphy wrote:
> On 2022-06-21 08:18, Janne Grunau wrote:
> > From: Sven Peter <sven@...npeter.dev>
> > 
> > The DARTs present in the M1 Pro/Max/Ultra SoC use a diffent PTE format.
> > They support a 42bit physical address space by shifting the paddr and
> > extending its mask inside the PTE.
> > They also come with mandatory sub-page protection now which we just
> > configure to always allow access to the entire page. This feature is
> > already present but optional on the previous DARTs which allows to
> > unconditionally configure it.
> > 
> > Signed-off-by: Sven Peter <sven@...npeter.dev>
> > Co-developed-by: Janne Grunau <j@...nau.net>
> > Signed-off-by: Janne Grunau <j@...nau.net>
> > 
> > ---
> > 
> > Changes in v3:
> > - apply change to io-pgtable-dart.c
> > - handle pte <> paddr conversion based on the pte format instead of
> >    the output address size
> > 
> > Changes in v2:
> > - add APPLE_DART2 PTE format
> > 
> >   drivers/iommu/io-pgtable-dart.c | 51 +++++++++++++++++++++++++++------
> >   drivers/iommu/io-pgtable.c      |  1 +
> >   include/linux/io-pgtable.h      |  1 +
> >   3 files changed, 45 insertions(+), 8 deletions(-)
> > 
> [...]
> > @@ -536,7 +571,7 @@ apple_dart_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
> >   	if (!cfg->coherent_walk)
> >   		return NULL;
> > -	if (cfg->oas > 36)
> > +	if (cfg->oas != 36 && cfg->oas != 42)
> >   		return NULL;
> 
> Wouldn't it make sense to tie this to the format? Maybe 36-bit OAS is still
> valid with v2, but presumably 42-bit with v1 definitely isn't.

The format is not know inside the alloc call unless I add per format 
alloc wrapper. I think we can trust the caller for now.

Janne