Message-ID: <3b2746f7779aa5dc39a406593dae37c4a8da676d.camel@redhat.com>
Date: Tue, 23 Jan 2024 11:23:20 +0100
From: Philipp Stanner <pstanner@...hat.com>
To: Jonathan Corbet <corbet@....net>, Hans de Goede <hdegoede@...hat.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Bjorn Helgaas
 <bhelgaas@...gle.com>, Sam Ravnborg <sam@...nborg.org>, dakr@...hat.com
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v2 00/10] Make PCI's devres API more consistent

Forgot to add a few changes to the changelog:

On Tue, 2024-01-23 at 10:42 +0100, Philipp Stanner wrote:
> Changes in v2:
>   - Make commit head lines congruent with PCI's style (Bjorn)
>   - Add missing error checks for devm_add_action(). (Andy)
>   - Repair the "Returns: " marks for docu generation (Andy)
>   - Initialize the addr_devres struct with memset(). (Andy)
>   - Make pcim_intx() a PCI-internal function so that new drivers
> won't
>     be encouraged to use the outdated pci_intx() mechanism.
>     (Andy / Philipp)
>   - Fix grammar and spelling (Bjorn)
>   - Be more precise on why pcim_iomap_table() is problematic (Bjorn)
>   - Provide the actual structs' and functions' names in the commit
>     messages (Bjorn)
>   - Remove redundant variable initializers (Andy)
>   - Regroup PM bitfield members in struct pci_dev (Andy)
>   - Consistently use the term "PCI devres API"; also in Patch #10
> (Bjorn)

 * Make pcim_intx() visible only for the PCI subsystem so that new    
   drivers won't use this outdated API (Andy, Myself)
 * Add a NOTE to pcim_iomap() to warn about this function being the    onee
   xception that does just return NULL.

This v2 now contains most of the feedback, except the ones Andy and I
haven't agreed on yet.

Thx,
P.

> 
> 
> ¡Hola!
> 
> PCI's devres API suffers several weaknesses:
> 
> 1. There are functions prefixed with pcim_. Those are always managed
>    counterparts to never-managed functions prefixed with pci_ – or so
> one
>    would like to think. There are some apparently unmanaged functions
>    (all region-request / release functions, and pci_intx()) which
>    suddenly become managed once the user has initialized the device
> with
>    pcim_enable_device() instead of pci_enable_device(). This
> "sometimes
>    yes, sometimes no" nature of those functions is confusing and
>    therefore bug-provoking. In fact, it has already caused a bug in
> DRM.
>    The last patch in this series fixes that bug.
> 2. iomappings: Instead of giving each mapping its own callback, the
>    existing API uses a statically allocated struct tracking one
> mapping
>    per bar. This is not extensible. Especially, you can't create
>    _ranged_ managed mappings that way, which many drivers want.
> 3. Managed request functions only exist as "plural versions" with a
>    bit-mask as a parameter. That's quite over-engineered considering
>    that each user only ever mapps one, maybe two bars.
> 
> This series:
> - add a set of new "singular" devres functions that use devres the
> way
>   its intended, with one callback per resource.
> - deprecates the existing iomap-table mechanism.
> - deprecates the hybrid nature of pci_ functions.
> - preserves backwards compatibility so that drivers using the
> existing
>   API won't notice any changes.
> - adds documentation, especially some warning users about the
>   complicated nature of PCI's devres.
> 
> 
> Note that this series is based on my "unify pci_iounmap"-series from
> a
> few weeks ago. [1]
> 
> I tested this on a x86 VM with a simple pci test-device with two
> regions. Operates and reserves resources as intended on my system.
> Kasan and kmemleak didn't find any problems.
> 
> I believe this series cleans the API up as much as possible without
> having to port all existing drivers to the new API. Especially, I
> think
> that this implementation is easy to extend if the need for new
> managed
> functions arises :)
> 
> Greetings,
> P.
> 
> Philipp Stanner (10):
>   PCI: add new set of devres functions
>   PCI: deprecate iomap-table functions
>   PCI: warn users about complicated devres nature
>   PCI: make devres region requests consistent
>   PCI: move dev-enabled status bit to struct pci_dev
>   PCI: move pinned status bit to struct pci_dev
>   PCI: give pcim_set_mwi() its own devres callback
>   PCI: give pci(m)_intx its own devres callback
>   PCI: remove legacy pcim_release()
>   drm/vboxvideo: fix mapping leaks
> 
>  Documentation/driver-api/pci/pci.rst  |    3 +
>  drivers/gpu/drm/vboxvideo/vbox_main.c |   24 +-
>  drivers/pci/devres.c                  | 1015 +++++++++++++++++++++--
> --
>  drivers/pci/iomap.c                   |   18 +
>  drivers/pci/pci.c                     |  123 ++-
>  drivers/pci/pci.h                     |   25 +-
>  include/linux/pci.h                   |   18 +-
>  7 files changed, 1011 insertions(+), 215 deletions(-)
> 

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