| Message ID | 1435195342-26879-6-git-send-email-mcgrof@do-not-panic.com |
|---|---|
| State | Not Applicable |
| Headers | show |
On Wed, Jun 24, 2015 at 06:22:18PM -0700, Luis R. Rodriguez wrote: > From: "Luis R. Rodriguez" <mcgrof@suse.com> > > PCI BARs tell us whether prefetching is safe, but they don't say anything > about write combining (WC). WC changes ordering rules and allows writes to > be collapsed, so it's not safe in general to use it on a prefetchable > region. > > Add pci_iomap_wc() and pci_iomap_wc_range() so drivers can take advantage > of write combining when they know it's safe. > > On architectures that don't fully support WC, e.g., x86 without PAT, > drivers for legacy framebuffers may get some of the benefit by using > arch_phys_wc_add() in addition to pci_iomap_wc(). But arch_phys_wc_add() > is unreliable and should be avoided in general. On x86, it uses MTRRs, > which are limited in number and size, so the results will vary based on > driver loading order. > > The goals of adding pci_iomap_wc() are to: > > - Give drivers an architecture-independent way to use WC so they can stop > using interfaces like mtrr_add() (on x86, pci_iomap_wc() uses > PAT when available) > > - Move toward using _PAGE_CACHE_MODE_UC, not _PAGE_CACHE_MODE_UC_MINUS, > on x86 on ioremap_nocache() (see de33c442ed2a ("x86 PAT: fix > performance drop for glx, use UC minus for ioremap(), ioremap_nocache() > and pci_mmap_page_range()") ... > diff --git a/lib/pci_iomap.c b/lib/pci_iomap.c > index bcce5f1..9604dcb 100644 > --- a/lib/pci_iomap.c > +++ b/lib/pci_iomap.c > @@ -52,6 +52,46 @@ void __iomem *pci_iomap_range(struct pci_dev *dev, > EXPORT_SYMBOL(pci_iomap_range); > > /** > + * pci_iomap_wc_range - create a virtual WC mapping cookie for a PCI BAR > + * @dev: PCI device that owns the BAR > + * @bar: BAR number > + * @offset: map memory at the given offset in BAR > + * @maxlen: max length of the memory to map > + * > + * Using this function you will get a __iomem address to your device BAR. > + * You can access it using ioread*() and iowrite*(). These functions hide > + * the details if this is a MMIO or PIO address space and will just do what > + * you expect from them in the correct way. When possible write combining > + * is used. > + * > + * @maxlen specifies the maximum length to map. If you want to get access to > + * the complete BAR from offset to the end, pass %0 here. > + * */ > +void __iomem *pci_iomap_wc_range(struct pci_dev *dev, > + int bar, > + unsigned long offset, > + unsigned long maxlen) > +{ > + resource_size_t start = pci_resource_start(dev, bar); > + resource_size_t len = pci_resource_len(dev, bar); > + unsigned long flags = pci_resource_flags(dev, bar); > + > + if (len <= offset || !start) > + return NULL; > + len -= offset; > + start += offset; > + if (maxlen && len > maxlen) > + len = maxlen; > + if (flags & IORESOURCE_IO) > + return NULL; I've moved this check at the beginning of the function so that we bail out before doing the computations above it.
On Thu, Jun 25, 2015 at 8:09 AM, Borislav Petkov <bp@suse.de> wrote: >> +void __iomem *pci_iomap_wc_range(struct pci_dev *dev, >> + int bar, >> + unsigned long offset, >> + unsigned long maxlen) >> +{ >> + resource_size_t start = pci_resource_start(dev, bar); >> + resource_size_t len = pci_resource_len(dev, bar); >> + unsigned long flags = pci_resource_flags(dev, bar); >> + >> + if (len <= offset || !start) >> + return NULL; >> + len -= offset; >> + start += offset; >> + if (maxlen && len > maxlen) >> + len = maxlen; >> + if (flags & IORESOURCE_IO) >> + return NULL; > > I've moved this check at the beginning of the function so that we bail > out before doing the computations above it. That indeed looks like a good optimization. Luis -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/asm-generic/pci_iomap.h b/include/asm-generic/pci_iomap.h index 7389c87..b1e17fc 100644 --- a/include/asm-generic/pci_iomap.h +++ b/include/asm-generic/pci_iomap.h @@ -15,9 +15,13 @@ struct pci_dev; #ifdef CONFIG_PCI /* Create a virtual mapping cookie for a PCI BAR (memory or IO) */ extern void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long max); +extern void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long max); extern void __iomem *pci_iomap_range(struct pci_dev *dev, int bar, unsigned long offset, unsigned long maxlen); +extern void __iomem *pci_iomap_wc_range(struct pci_dev *dev, int bar, + unsigned long offset, + unsigned long maxlen); /* Create a virtual mapping cookie for a port on a given PCI device. * Do not call this directly, it exists to make it easier for architectures * to override */ @@ -34,12 +38,22 @@ static inline void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned lon return NULL; } +static inline void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long max) +{ + return NULL; +} static inline void __iomem *pci_iomap_range(struct pci_dev *dev, int bar, unsigned long offset, unsigned long maxlen) { return NULL; } +static inline void __iomem *pci_iomap_wc_range(struct pci_dev *dev, int bar, + unsigned long offset, + unsigned long maxlen) +{ + return NULL; +} #endif #endif /* __ASM_GENERIC_IO_H */ diff --git a/lib/pci_iomap.c b/lib/pci_iomap.c index bcce5f1..9604dcb 100644 --- a/lib/pci_iomap.c +++ b/lib/pci_iomap.c @@ -52,6 +52,46 @@ void __iomem *pci_iomap_range(struct pci_dev *dev, EXPORT_SYMBOL(pci_iomap_range); /** + * pci_iomap_wc_range - create a virtual WC mapping cookie for a PCI BAR + * @dev: PCI device that owns the BAR + * @bar: BAR number + * @offset: map memory at the given offset in BAR + * @maxlen: max length of the memory to map + * + * Using this function you will get a __iomem address to your device BAR. + * You can access it using ioread*() and iowrite*(). These functions hide + * the details if this is a MMIO or PIO address space and will just do what + * you expect from them in the correct way. When possible write combining + * is used. + * + * @maxlen specifies the maximum length to map. If you want to get access to + * the complete BAR from offset to the end, pass %0 here. + * */ +void __iomem *pci_iomap_wc_range(struct pci_dev *dev, + int bar, + unsigned long offset, + unsigned long maxlen) +{ + resource_size_t start = pci_resource_start(dev, bar); + resource_size_t len = pci_resource_len(dev, bar); + unsigned long flags = pci_resource_flags(dev, bar); + + if (len <= offset || !start) + return NULL; + len -= offset; + start += offset; + if (maxlen && len > maxlen) + len = maxlen; + if (flags & IORESOURCE_IO) + return NULL; + if (flags & IORESOURCE_MEM) + return ioremap_wc(start, len); + /* What? */ + return NULL; +} +EXPORT_SYMBOL_GPL(pci_iomap_wc_range); + +/** * pci_iomap - create a virtual mapping cookie for a PCI BAR * @dev: PCI device that owns the BAR * @bar: BAR number @@ -70,4 +110,25 @@ void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long maxlen) return pci_iomap_range(dev, bar, 0, maxlen); } EXPORT_SYMBOL(pci_iomap); + +/** + * pci_iomap_wc - create a virtual WC mapping cookie for a PCI BAR + * @dev: PCI device that owns the BAR + * @bar: BAR number + * @maxlen: length of the memory to map + * + * Using this function you will get a __iomem address to your device BAR. + * You can access it using ioread*() and iowrite*(). These functions hide + * the details if this is a MMIO or PIO address space and will just do what + * you expect from them in the correct way. When possible write combining + * is used. + * + * @maxlen specifies the maximum length to map. If you want to get access to + * the complete BAR without checking for its length first, pass %0 here. + * */ +void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long maxlen) +{ + return pci_iomap_wc_range(dev, bar, 0, maxlen); +} +EXPORT_SYMBOL_GPL(pci_iomap_wc); #endif /* CONFIG_PCI */