linux-kernel - Re: [PATCH 00/11] PCI: Resizable BAR improvements

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Message-ID: <bfb8fa6f-1217-411f-88c0-24788a0c15c9@amd.com>
Date: Thu, 11 Sep 2025 10:35:18 +0200
From: Christian König <christian.koenig@....com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
 Krzysztof Wilczyński <kw@...ux.com>,
 Michał Winiarski <michal.winiarski@...el.com>,
 Alex Deucher <alexander.deucher@....com>, amd-gfx@...ts.freedesktop.org,
 David Airlie <airlied@...il.com>, dri-devel@...ts.freedesktop.org,
 intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Simona Vetter <simona@...ll.ch>,
 Tvrtko Ursulin <tursulin@...ulin.net>,
 ?UTF-8?q?Thomas=20Hellstr=C3=B6m?= <thomas.hellstrom@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH 00/11] PCI: Resizable BAR improvements

On 11.09.25 09:55, Ilpo Järvinen wrote:
> pci.c has been used as catch everything that doesn't fits elsewhere
> within PCI core and thus resizable BAR code has been placed there as
> well. Move Resizable BAR related code to a newly introduced rebar.c to
> reduce size of pci.c. After move, there are no pci_rebar_*() calls from
> pci.c indicating this is indeed well-defined subset of PCI core.
> 
> Endpoint drivers perform Resizable BAR related operations which could
> well be performed by PCI core to simplify driver-side code. This
> series adds a few new API functions to that effect and converts the
> drivers to use the new APIs (in separate patches).
> 
> While at it, also convert BAR sizes bitmask to u64 as PCIe spec already
> specifies more sizes than what will fit u32 to make the API typing more
> future-proof. The extra sizes beyond 128TB are not added at this point.
> 
> These are based on pci/main, there are two minor conflicts with the
> work in pci/resource but I'm hesitant to base this on top of it as this
> is otherwise entirely independent. If we end up having to pull the
> bridge window select changes, there should be no reason why this does
> have to become collateral damage (so my suggestion, if this is good to
> go in this cycle, to take this into a separate branch than pci/resource
> and deal with those small conflicts while merging into pci/next).
> 
> I've tested sysfs resize, i915, and xe BAR resizing functionality. In
> the case of xe, I did small hack patch as its resize is anyway broken
> as is because BAR0 pins the bridge window so resizing BAR2 fails. My
> hack caused other problems further down the road (likely because BAR0
> is in use by the driver so releasing it messed assumptions xe driver
> has) but the BAR resize itself was working which was all I was
> interested to know. I'm not planning to pursue fixing the pinning
> problem within xe driver because the core changes to consider maximum
> size of the resizable BARs should take care of the main problem by
> different means.
> 
> Some parts of this are to be used by the resizable BAR changes into the
> resource fitting/assingment logic but these seem to stand on their own
> so sending these out now to reduce the size of the other patch series.

Yeah, sounds like a good idea to me.

Before I answer each mail individually:

Patches #1-#3, #8, #10 and #11 are Reviewed-by: Christian König <christian.koenig@....com>.

Patches #6, #7 and #9 are Acked-by: Christian König <christian.koenig@....com>.

Nit pick comments on patches #4 and #5, feel free to add my rb to them as well when those are fixed.

Regards,
Christian.

> 
> 
> Ilpo Järvinen (11):
>   PCI: Move Resizable BAR code into rebar.c
>   PCI: Cleanup pci_rebar_bytes_to_size() and move into rebar.c
>   PCI: Move pci_rebar_size_to_bytes() and export it
>   PCI: Improve Resizable BAR functions kernel doc
>   PCI: Add pci_rebar_size_supported() helper
>   drm/i915/gt: Use pci_rebar_size_supported()
>   drm/xe/vram: Use PCI rebar helpers in resize_vram_bar()
>   PCI: Add pci_rebar_get_max_size()
>   drm/xe/vram: Use pci_rebar_get_max_size()
>   drm/amdgpu: Use pci_rebar_get_max_size()
>   PCI: Convert BAR sizes bitmasks to u64
> 
>  Documentation/driver-api/pci/pci.rst        |   3 +
>  drivers/gpu/drm/amd/amdgpu/amdgpu_device.c  |   8 +-
>  drivers/gpu/drm/i915/gt/intel_region_lmem.c |  10 +-
>  drivers/gpu/drm/xe/xe_vram.c                |  32 +-
>  drivers/pci/Makefile                        |   2 +-
>  drivers/pci/iov.c                           |   9 +-
>  drivers/pci/pci-sysfs.c                     |   2 +-
>  drivers/pci/pci.c                           | 145 ---------
>  drivers/pci/pci.h                           |   5 +-
>  drivers/pci/rebar.c                         | 318 ++++++++++++++++++++
>  drivers/pci/setup-res.c                     |  78 -----
>  include/linux/pci.h                         |  15 +-
>  12 files changed, 354 insertions(+), 273 deletions(-)
>  create mode 100644 drivers/pci/rebar.c
> 
> 
> base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585