linux-kernel - Re: [PATCH v5 2/7] iommu: Decouple iommu

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Message-ID: <20231012123755.GH3952@nvidia.com>
Date:   Thu, 12 Oct 2023 09:37:55 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>, joro@...tes.org,
        will@...nel.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/7] iommu: Decouple iommu_present() from bus ops

On Thu, Oct 12, 2023 at 12:40:01PM +0100, Robin Murphy wrote:
> On 2023-10-12 07:05, Baolu Lu wrote:
> > On 10/12/23 2:14 AM, Robin Murphy wrote:
> > > Much as I'd like to remove iommu_present(), the final remaining users
> > > are proving stubbornly difficult to clean up, so kick that can down the
> > > road and just rework it to preserve the current behaviour without
> > > depending on bus ops. Since commit 57365a04c921 ("iommu: Move bus setup
> > 
> > The iommu_present() is only used in below two drivers.
> > 
> > $ git grep iommu_present
> > drivers/gpu/drm/mediatek/mtk_drm_drv.c: if
> > (!iommu_present(&platform_bus_type))
> > drivers/gpu/drm/tegra/drm.c:    if (host1x_drm_wants_iommu(dev) &&
> > iommu_present(&platform_bus_type)) {
> > 
> > Both are platform drivers and have the device pointer passed in. Just
> > out of curiosity, why not replacing them with device_iommu_mapped()
> > instead? Sorry if I overlooked previous discussion.
> 
> Yes, we've already gone round in circles on this several times, that's why
> it's explicitly called out as "stubbornly difficult" in the commit message.
> The Mediatek one is entirely redundant, but it seems I have yet to figure
> out the right CC list to get anyone to care about that patch[1].

Please just have Joerg take such a trivial patch, there is no reason
we need to torture outselves because DRM side is not behaving well. :(

Jason