linux-kernel - Re: [PATCH] fsl_pamu: Use 40-bits for addressing where appropriate

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Message-ID: <2025042218-beneficial-wildcat-77dd3e@boujee-and-buff>
Date: Tue, 22 Apr 2025 18:21:32 -0400
From: Ben Collins <ben.collins@...ux.dev>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: iommu@...ts.linux.dev, Joerg Roedel <joro@...tes.org>, 
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>, 
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] fsl_pamu: Use 40-bits for addressing where appropriate

On Tue, Apr 22, 2025 at 04:09:21PM -0500, Jason Gunthorpe wrote:
> On Mon, Apr 21, 2025 at 10:46:19PM -0400, Ben Collins wrote:
> > diff --git a/drivers/iommu/fsl_pamu_domain.c b/drivers/iommu/fsl_pamu_domain.c
> > index 30be786bff11e..a4bc6482a00f7 100644
> > --- a/drivers/iommu/fsl_pamu_domain.c
> > +++ b/drivers/iommu/fsl_pamu_domain.c
> > @@ -214,9 +214,10 @@ static struct iommu_domain *fsl_pamu_domain_alloc(unsigned type)
> >  	INIT_LIST_HEAD(&dma_domain->devices);
> >  	spin_lock_init(&dma_domain->domain_lock);
> >  
> > -	/* default geometry 64 GB i.e. maximum system address */
> > +	/* Set default geometry based on physical address limit. */
> >  	dma_domain->iommu_domain. geometry.aperture_start = 0;
> > -	dma_domain->iommu_domain.geometry.aperture_end = (1ULL << 36) - 1;
> > +	dma_domain->iommu_domain.geometry.aperture_end =
> > +		(1ULL << PAMU_MAX_PHYS_BITS) - 1;
> >  	dma_domain->iommu_domain.geometry.force_aperture = true;
> 
> What on earth does this even do? There is no map_range() callback in
> this driver, so nothing should be reading geometry..

I dunno, but your "FIXME this is broken" comments are all over it from a
year and a half ago:

Author: Jason Gunthorpe <jgg@...pe.ca>
Date:   Wed Sep 13 10:43:38 2023 -0300

    iommu/fsl_pamu: Implement a PLATFORM domain

       /*
        * FIXME: This isn't creating an unmanaged domain since the
        * default_domain_ops do not have any map/unmap function it doesn't meet
        * the requirements for __IOMMU_DOMAIN_PAGING. The only purpose seems to
        * allow drivers/soc/fsl/qbman/qman_portal.c to do
        * fsl_pamu_configure_l1_stash()
        */

The logic hasn't really been touched in 10 years.

-- 
 Ben Collins
 https://libjwt.io
 https://github.com/benmcollins
 --
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