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    SubjectRe: [RFT PATCH v3 08/27] asm-generic/io.h: Add a non-posted variant of ioremap()
    On Fri, Mar 05, 2021 at 06:38:43AM +0900, Hector Martin wrote:
    > ARM64 currently defaults to posted MMIO (nGnRnE), but some devices
    > require the use of non-posted MMIO (nGnRE). Introduce a new ioremap()
    > variant to handle this case. ioremap_np() is aliased to ioremap() by
    > default on arches that do not implement this variant.
    >
    > sparc64 is the only architecture that needs to be touched directly,
    > because it includes neither of the generic io.h or iomap.h headers.
    >
    > This adds the IORESOURCE_MEM_NONPOSTED flag, which maps to this
    > variant and marks a given resource as requiring non-posted mappings.
    > This is implemented in the resource system because it is a SoC-level
    > requirement, so existing drivers do not need special-case code to pick
    > this ioremap variant.
    >
    > Then this is implemented in devres by introducing devm_ioremap_np(),
    > and making devm_ioremap_resource() automatically select this variant
    > when the resource has the IORESOURCE_MEM_NONPOSTED flag set.
    >
    > Signed-off-by: Hector Martin <marcan@marcan.st>
    > ---
    > .../driver-api/driver-model/devres.rst | 1 +
    > arch/sparc/include/asm/io_64.h | 4 ++++
    > include/asm-generic/io.h | 22 ++++++++++++++++++-
    > include/asm-generic/iomap.h | 9 ++++++++
    > include/linux/io.h | 2 ++
    > include/linux/ioport.h | 1 +
    > lib/devres.c | 22 +++++++++++++++++++
    > 7 files changed, 60 insertions(+), 1 deletion(-)
    >
    > diff --git a/Documentation/driver-api/driver-model/devres.rst b/Documentation/driver-api/driver-model/devres.rst
    > index cd8b6e657b94..2f45877a539d 100644
    > --- a/Documentation/driver-api/driver-model/devres.rst
    > +++ b/Documentation/driver-api/driver-model/devres.rst
    > @@ -309,6 +309,7 @@ IOMAP
    > devm_ioremap()
    > devm_ioremap_uc()
    > devm_ioremap_wc()
    > + devm_ioremap_np()
    > devm_ioremap_resource() : checks resource, requests memory region, ioremaps
    > devm_ioremap_resource_wc()
    > devm_platform_ioremap_resource() : calls devm_ioremap_resource() for platform device
    > diff --git a/arch/sparc/include/asm/io_64.h b/arch/sparc/include/asm/io_64.h
    > index 9bb27e5c22f1..9fbfc9574432 100644
    > --- a/arch/sparc/include/asm/io_64.h
    > +++ b/arch/sparc/include/asm/io_64.h
    > @@ -409,6 +409,10 @@ static inline void __iomem *ioremap(unsigned long offset, unsigned long size)
    > #define ioremap_uc(X,Y) ioremap((X),(Y))
    > #define ioremap_wc(X,Y) ioremap((X),(Y))
    > #define ioremap_wt(X,Y) ioremap((X),(Y))
    > +static inline void __iomem *ioremap_np(unsigned long offset, unsigned long size)
    > +{
    > + return NULL;
    > +}
    >
    > static inline void iounmap(volatile void __iomem *addr)
    > {
    > diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
    > index c6af40ce03be..082e0c96db6e 100644
    > --- a/include/asm-generic/io.h
    > +++ b/include/asm-generic/io.h
    > @@ -942,7 +942,9 @@ static inline void *phys_to_virt(unsigned long address)
    > *
    > * ioremap_wc() and ioremap_wt() can provide more relaxed caching attributes
    > * for specific drivers if the architecture choses to implement them. If they
    > - * are not implemented we fall back to plain ioremap.
    > + * are not implemented we fall back to plain ioremap. Conversely, ioremap_np()
    > + * can provide stricter non-posted write semantics if the architecture
    > + * implements them.
    > */
    > #ifndef CONFIG_MMU
    > #ifndef ioremap
    > @@ -993,6 +995,24 @@ static inline void __iomem *ioremap_uc(phys_addr_t offset, size_t size)
    > {
    > return NULL;
    > }
    > +
    > +/*
    > + * ioremap_np needs an explicit architecture implementation, as it
    > + * requests stronger semantics than regular ioremap(). Portable drivers
    > + * should instead use one of the higher-level abstractions, like
    > + * devm_ioremap_resource(), to choose the correct variant for any given
    > + * device and bus. Portable drivers with a good reason to want non-posted
    > + * write semantics should always provide an ioremap() fallback in case
    > + * ioremap_np() is not available.
    > + */
    > +#ifndef ioremap_np
    > +#define ioremap_np ioremap_np
    > +static inline void __iomem *ioremap_np(phys_addr_t offset, size_t size)
    > +{
    > + return NULL;
    > +}
    > +#endif

    Can we implement the generic pci_remap_cfgspace() in terms of ioremap_np()
    if it is supported by the architecture? That way, we could avoid defining
    both on arm64.

    Will

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