On Mon, Jan 15, 2024 at 03:46:12PM +0100, Philipp Stanner wrote: > PCI's devres API is not extensible to ranged mappings and has > bug-provoking features. Improve that by providing better alternatives. I guess "ranged mappings" means a mapping that doesn't cover an entire BAR? Maybe there's a way to clarify? > When the original devres API for PCI was implemented, priority was given > to the creation of a set of "pural functions" such as > pcim_request_regions(). These functions have bit masks as parameters to > specify which BARs shall get mapped. Most users, however, only use those > to mapp 1-3 BARs. > A complete set of "singular functions" does not exist. s/mapp/map/ Rewrap to fill 75 columns or add blank lines between paragraphs. Also below. > As functions mapping / requesting multiple BARs at once have (almost) no > mechanism in C to return the resources to the caller of the plural > function, the devres API utilizes the iomap-table administrated by the > function pcim_iomap_table(). > > The entire PCI devres implementation was strongly tied to that table > which only allows for mapping whole, complete BARs, as the BAR's index > is used as table index. Consequently, it's not possible to, e.g., have a > pcim_iomap_range() function with that mechanism. > > An additional problem is that pci-devres has been ipmlemented in a sort > of "hybrid-mode": Some unmanaged functions have managed counterparts > (e.g.: pci_iomap() <-> pcim_iomap()), making their managed nature > obvious to the programmer. However, the region-request functions in > pci.c, prefixed with pci_, behave either managed or unmanaged, depending > on whether pci_enable_device() or pcim_enable_device() has been called > in advance. s/ipmlemented/implemented/ > This hybrid API is confusing and should be more cleanly separated by > providing always-managed functions prefixed with pcim_. > > Thus, the existing devres API is not desirable because: > a) The vast majority of the users of the plural functions only > ever sets a single bit in the bit mask, consequently making > them singular functions anyways. > b) There is no mechanism to request / iomap only part of a BAR. > c) The iomap-table mechanism is over-engineered, complicated and > can by definition not perform bounds checks, thus, provoking > memory faults: pcim_iomap_table(pdev)[42] Not sure what "pcim_iomap_table(pdev)[42]" means. > d) region-request functions being sometimes managed and > sometimes not is bug-provoking. Indent with spaces (not tabs) so it still looks good when "git log" adds spaces to indent. > + * Legacy struct storing addresses to whole mapped bars. s/bar/BAR/ (several places). > + /* A region spaning an entire bar. */ > + PCIM_ADDR_DEVRES_TYPE_REGION, > + > + /* A region spaning an entire bar, and a mapping for that whole bar. */ > + PCIM_ADDR_DEVRES_TYPE_REGION_MAPPING, > + > + /* > + * A mapping within a bar, either spaning the whole bar or just a range. > + * Without a requested region. s/spaning/spanning/ (several places). > + if (start == 0 || len == 0) /* that's an unused BAR. */ s/that/That/ > + /* > + * Ranged mappings don't get added to the legacy-table, since the table > + * only ever keeps track of whole BARs. > + */ > + Spurious blank line. > + devres_add(&pdev->dev, res); > + return mapping; > +} > +EXPORT_SYMBOL(pcim_iomap_range); Bjorn
