[PATCH v9 00/13] Make PCI's devres API more consistent

Thu Jun 13 11:50:13 UTC 2024

Changes in v9:
  - Remove forgotten dead code ('enabled' bit in struct pci_dev) in
    patch No.8 ("Move pinned status bit...")
  - Rework patch No.3:
      - Change title from "Reimplement plural devres functions"
        to "Add partial-BAR devres support".
      - Drop excessive details about the general cleanup from the commit
	message. Only motivate why this patch's new infrastructure is
	necessary.
  - Fix some minor spelling issues (s/pci/PCI ...)

Changes in v8:
  - Rebase the series on the already merged patches which were slightly
    modified by Bjorn Helgaas.
  - Reword the pci_intx() commit message so it clearly states it's about
    reworking pci_intx().
  - Move the removal of find_pci_dr() from patch "Remove legacy
    pcim_release()" to patch "Give pci_intx() its own devres callback"
    since this later patch already removed all calls to that function.
  - In patch "Give pci_intx() its own devres callback": use
    pci_is_enabled() (and, thus, the enabled_cnt in struct pci_dev)
    instead of a separate enabled field. (Bjorn)

Changes in v7:
  - Split the entire series in smaller, more atomic chunks / patches
    (Bjorn)
  - Remove functions (such as pcim_iomap_region_range()) that do not yet
    have a user (Bjorn)
  - Don't export interfaces publicly anymore, except for
    pcim_iomap_range(), needed by vboxvideo (Bjorn)
  - Mention the actual (vboxvideo) bug in "PCI: Warn users..." commit
    (Bjorn)
  - Drop docstring warnings on PCI-internal functions (Bjorn)
  - Rework docstring warnings
  - Fix spelling in a few places. Rewrapp paragraphs (Bjorn)

Changes in v6:
  - Restructure the cleanup in pcim_iomap_regions_request_all() so that
    it doesn't trigger a (false positive) test robot warning. No
    behavior change intended. (Dan Carpenter)

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  - Remove the comment advising to call (the outdated) pcim_intx() in pci.c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 one
    exception 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 (13):
  PCI: Add and use devres helper for bit masks
  PCI: Add devres helpers for iomap table
  PCI: Add partial-BAR devres support
  PCI: Deprecate two surplus devres functions
  PCI: Make devres region requests consistent
  PCI: Warn users about complicated devres nature
  PCI: Remove enabled status bit from pci_devres
  PCI: Move pinned status bit to struct pci_dev
  PCI: Give pcim_set_mwi() its own devres callback
  PCI: Give pci_intx() its own devres callback
  PCI: Remove legacy pcim_release()
  PCI: Add pcim_iomap_range()
  drm/vboxvideo: fix mapping leaks

 drivers/gpu/drm/vboxvideo/vbox_main.c |  20 +-
 drivers/pci/devres.c                  | 903 +++++++++++++++++++++-----
 drivers/pci/iomap.c                   |  16 +
 drivers/pci/pci.c                     |  94 ++-
 drivers/pci/pci.h                     |  23 +-
 include/linux/pci.h                   |   5 +-
 6 files changed, 858 insertions(+), 203 deletions(-)

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2.45.0