linux-kernel - Re: [PATCH v4 1/2] iommu/io-pgtable-arm: Add way to debug pgtable walk

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Date: Wed, 19 Jun 2024 13:33:07 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Robin Murphy <robin.murphy@....com>
Cc: Rob Clark <robdclark@...il.com>, Will Deacon <will@...nel.org>,
	linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
	Rob Clark <robdclark@...omium.org>, Joerg Roedel <joro@...tes.org>,
	Boris Brezillon <boris.brezillon@...labora.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Joao Martins <joao.m.martins@...cle.com>,
	"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
	"open list:IOMMU SUBSYSTEM" <iommu@...ts.linux.dev>,
	open list <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v4 1/2] iommu/io-pgtable-arm: Add way to debug pgtable
 walk

On Mon, Jun 17, 2024 at 04:13:41PM +0100, Robin Murphy wrote:
> On 23/05/2024 6:52 pm, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> > 
> > Add an io-pgtable method to walk the pgtable returning the raw PTEs that
> > would be traversed for a given iova access.
> 
> Have to say I'm a little torn here - with my iommu-dma hat on I'm not super
> enthusiastic about adding any more overhead to iova_to_phys, but in terms of
> maintaining io-pgtable I do like the overall shape of the implementation...

If you mark arm_lpae_pgtable_walk() and the callbacks as
__always_inline then the compiler should generate the same code as
today for arm_lpae_iova_to_phys().

Jason