Re: [PATCH v6 00/10] Make PCI's devres API more consistent

Bjorn Helgaas
2024-04-24T20:12:31Z

On Mon, Apr 08, 2024 at 10:44:12AM +0200, Philipp Stanner wrote:
> ...
> 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.

There's a lot of good work here; thanks for working on it.

> Philipp Stanner (10):
> PCI: Add new set of devres functions

This first patch adds some infrastructure and several new exported
interfaces:

void __iomem *pcim_iomap_region(struct pci_dev *pdev, int bar, const char *name)
void pcim_iounmap_region(struct pci_dev *pdev, int bar)
int pcim_request_region(struct pci_dev *pdev, int bar, const char *name)
void pcim_release_region(struct pci_dev *pdev, int bar)
void __iomem *pcim_iomap_range(struct pci_dev *pdev, int bar,
void __iomem *pcim_iomap_region_range(struct pci_dev *pdev, int bar,
void pcim_iounmap_region_range(struct pci_dev *pdev, int bar,

> PCI: Deprecate iomap-table functions

This adds a little bit of infrastructure (add/remove to legacy_table),
reimplements these existing interfaces:

void __iomem *pcim_iomap(struct pci_dev *pdev, int bar, unsigned long maxlen)
void pcim_iounmap(struct pci_dev *pdev, void __iomem *addr)
int pcim_iomap_regions(struct pci_dev *pdev, int mask, const char *name)
int pcim_iomap_regions_request_all(struct pci_dev *pdev, int mask,
void pcim_iounmap_regions(struct pci_dev *pdev, int mask)

and adds a couple new exported interfaces:

void pcim_release_all_regions(struct pci_dev *pdev)
int pcim_request_all_regions(struct pci_dev *pdev, const char *name)

There's a lot going on in these two patches, so they're hard to
review. I think it would be easier if you could do the fixes to
existing interfaces first, followed by adding new things, maybe
something like separate patches that:

- Add pcim_addr_devres_alloc(), pcim_addr_devres_free(),
pcim_addr_devres_clear().

- Add pcim_add_mapping_to_legacy_table(),
pcim_remove_mapping_from_legacy_table(),
pcim_remove_bar_from_legacy_table().

- Reimplement pcim_iomap(), pcim_iomap_regions(), pcim_iounmap().

- Add new interfaces like pcim_iomap_region(),
pcim_request_region(), etc.

AFAICS, except for pcim_iomap_range() (used by vbox), these new
interfaces have no users outside drivers/pci, so ... we might
defer adding them, or at least defer exposing them via
include/linux/pci.h, until we have users for them.

> 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 | 1011 +++++++++++++++++++++----
> drivers/pci/iomap.c | 18 +
> drivers/pci/pci.c | 123 ++-
> drivers/pci/pci.h | 21 +-
> include/linux/pci.h | 18 +-
> 6 files changed, 999 insertions(+), 212 deletions(-)
>
> --
> 2.44.0
>