linux-kernel - Re: [PATCH v3 00/11] PCI: Resizable BAR improvements

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Message-ID: <w35eozxuh3netnt5kdwuqp7bespytvsyn2smznlrcigjb24eeh@amk26j7ihnpl>
Date: Thu, 23 Oct 2025 17:02:42 -0500
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	<linux-pci@...r.kernel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, Krzysztof
 Wilczyński <kw@...ux.com>, Christian König
	<christian.koenig@....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>, Rodrigo Vivi
	<rodrigo.vivi@...el.com>, Simona Vetter <simona@...ll.ch>, Tvrtko Ursulin
	<tursulin@...ulin.net>, "Michael J . Ruhl" <mjruhl@...ana.ai>, Andi Shyti
	<andi.shyti@...ux.intel.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 00/11] PCI: Resizable BAR improvements

On Thu, Oct 23, 2025 at 04:29:43PM -0500, Bjorn Helgaas wrote:
>On Wed, Oct 22, 2025 at 04:33:20PM +0300, 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.
>>
>> 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.
>>
>> v3:
>> - Rebased to solve minor conflicts
>>
>> v2: https://lore.kernel.org/linux-pci/20250915091358.9203-1-ilpo.jarvinen@linux.intel.com/
>> - Kerneldoc:
>>   - Improve formatting of errno returns
>>   - Open "ctrl" -> "control"
>>   - Removed mislead "bit" words (when referring to BAR size)
>>   - Rewrote pci_rebar_get_possible_sizes() kernel doc to not claim the
>>     returned bitmask is defined in PCIe spec as the capability bits now
>>     span across two registers in the spec and are not continuous (we
>>     don't support the second block of bits yet, but this API is expected
>>     to return the bits without the hole so it will not be matching with
>>     the spec layout).
>> - Dropped superfluous zero check from pci_rebar_size_supported()
>> - Small improvement to changelog of patch 7
>>
>> 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                         | 314 ++++++++++++++++++++
>>  drivers/pci/setup-res.c                     |  78 -----
>>  include/linux/pci.h                         |  15 +-
>>  12 files changed, 350 insertions(+), 273 deletions(-)
>>  create mode 100644 drivers/pci/rebar.c
>
>Applied to pci/rebar for v6.18, thanks, Ilpo!

is this for v6.18 or it's a typo and it's going to v6.19?

>
>If we have follow-on resource assignment changes that depend on these,
>maybe I'll rename the branch to be more generic before applying them.
>
>Also applied the drivers/gpu changes based on the acks.  I see the CI
>merge failures since this series is based on v6.18-rc1; I assume the
>CI applies to current linux-next or similar.  I'll check the conflicts

it tries on drm-tip that contains drm-xe-next going to v6.19. We have
some changes there that conflict, but shouldn't be hard.

We also need https://lore.kernel.org/linux-pci/20250918-xe-pci-rebar-2-v1-1-6c094702a074@intel.com/
to actually fix the rebar in some cases. Could you take a look?

thanks
Lucas De Marchi

>later and we can defer those changes if needed.