[v5,00/10] Make PCI's devres API more consistent

Message

Philipp Stanner April 3, 2024, 8:07 a.m. UTC

I now regard this to be the final version of my cleanup, hoping that we
can make it to Linux 6.10 – otherwise this would end up blocking my
other work for another release cycle.

@Heiner:
Thx for the feedback on the other list. Since none of that was
fundamental (bugs, errors and so on) I suggest we postpone further
improvements of the PCI devres API to a release cycle following 6.10.
Maybe we could then even try to port drivers using the old API, removing
that one entirely.

Changes in v5:
  - Add Hans's Reviewed-by to vboxvideo patch (Hans de Goede)
  - Remove stable-kernel from CC in vboxvideo patch (Hans de Goede)

Changes in v4:
  - Rebase against linux-next

Changes in v3:
  - Use the term "PCI devres API" at some forgotten places.
  - Fix more grammar errors in patch #3.
  - Remove the comment advising to call (the outdated) pcim_intx() in pci.c
  - Rename __pcim_request_region_range() flags-field "exclusive" to
    "req_flags", since this is what the int actually represents.
  - Remove the call to pcim_region_request() from patch #10. (Hans)

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    be encouraged to use the outdated pci_intx() mechanism.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)
  - 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    drivers won't use this outdated API (Andy, Myself)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.
  - Consistently use the term "PCI devres API"; also in Patch #10 (Bjorn)


¡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

 drivers/gpu/drm/vboxvideo/vbox_main.c |   20 +-
 drivers/pci/devres.c                  | 1013 +++++++++++++++++++++----
 drivers/pci/iomap.c                   |   18 +
 drivers/pci/pci.c                     |  123 ++-
 drivers/pci/pci.h                     |   21 +-
 include/linux/pci.h                   |   18 +-
 6 files changed, 1001 insertions(+), 212 deletions(-)