Re: [PATCH v3 00/32] PCI: fix config and I/O Address space memory mappings

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2017-04-11 at 13:28 +0100, Lorenzo Pieralisi wrote:
> This patch series[1] is a v3 of a previous version:
> 
> v2: https://lkml.org/lkml/2017/3/27/220

I am not a fan of this at All.

That whole concept of "ioremap_nopost" is simply not applicable to the
majority of architectures and certainly not in a way that can apply to
arbitrary mappings.

It's also very wrong to provide a "default" operation whose semantics
are weaker than what it's supposed to implement. Very wrong actually.
People will use it assuming the non-posted behaviour and things will
break in subtle way when it cannot be provided.

What exactly are you trying to fix here ?

If a given PCIe host bridge (architecture specific) require a special
sauce to provide the illusion of non-posting, then implement this in
the actual root complex code.

BTW. I'm pretty sure we "accidentally" made config writes posted at
least to the PHB on a number of powerpc systems forever and we *never*
had a problem because of it ;)

> v2 -> v3:
> 	- Created a default ioremap_nopost() implementation in a
> separate
> 	  asm-generic header and patched all arches to make use of it
> 	- Removed PCI drivers patches from the series to simplify the
> 	  review, they will be posted separately once the
> ioremap_nopost()
> 	  interface is settled
> 	- Fixed devm_ioremap_* BUS offset comments and implemented
> 	  nopost interface on top of it
> 	- Added collected tags
> 
> v1: https://lkml.org/lkml/2017/2/27/228
> 
> v1 -> v2:
> 	- Changed pci_remap_cfgspace() to more generic ioremap_nopost()
> 	  interface
> 	- Added pgprot_nonposted
> 	- Fixed build errors on arches not relying on asm-generic
> headers
> 	- Added PCI versatile host controller driver patch
> 	- Added missing config space remapping to hisilicon host
> controller
> 
> ---------------------
> Original cover letter
> ---------------------
> 
> PCI local bus specifications (Rev3.0, 3.2.5 "Transaction Ordering
> and Posting") strictly require PCI configuration and I/O Address
> space
> write transactions to be non-posted.
> 
> Current crop of DT/ACPI PCI host controllers drivers relies on
> the ioremap interface to map ECAM and ECAM-derivative PCI config
> regions and pci_remap_iospace() to create a VMA for mapping
> PCI host bridge I/O Address space transactions to CPU virtual address
> space.
> 
> On some platforms (ie ARM/ARM64) ioremap fails to comply with the PCI
> configuration non-posted write transactions requirement, because it
> provides a memory mapping that issues "bufferable" or, in PCI terms
> "posted" write transactions. Likewise, the current
> pci_remap_iospace()
> implementation maps the physical address range that the PCI
> translates
> to I/O space cycles to virtual address space through pgprot_device()
> attributes that on eg ARM64 provides a memory mapping issuing
> posted writes transactions, which is not PCI specifications
> compliant.
> 
> This patch series[1] addresses both issues in one go:
> 
> - It updates the pci_remap_iospace() function to use a page mapping
>   that guarantees non-posted write transactions for I/O space
> addresses
> - It adds a kernel API to remap PCI config space resources, so that
>   architecture can override it with a mapping implementation that
>   guarantees PCI specifications compliancy wrt non-posted write
>   configuration transactions
> - It updates all PCI host controller implementations (and the generic
>   ECAM layer) to use the newly introduced mapping interface
> 
> Tested on Juno ECAM based interface (DT/ACPI).
> 
> Non-ECAM PCI host controller drivers patches need checking to make
> sure that:
> 
> - I patched the correct resource region mapping for config space
> - There are not any other ways to ensure posted-write completion
>   in the respective pci_ops that make the relevant patch unnecessary
> 
> [1]
> git://git.kernel.org/pub/scm/linux/kernel/git/lpieralisi/linux.git
> pci/config-io-mappings-fix-v3
> 
> Lorenzo Pieralisi (32):
>   PCI: remove __weak tag from pci_remap_iospace()
>   asm-generic/pgtable.h: introduce pgprot_nonposted remap attribute
>   PCI: fix pci_remap_iospace() remap attribute
>   asm-generic: add ioremap_nopost() remap interface
>   alpha: include default ioremap_nopost() implementation
>   avr32: include default ioremap_nopost() implementation
>   arc: include default ioremap_nopost() implementation
>   cris: include default ioremap_nopost() implementation
>   frv: include default ioremap_nopost() implementation
>   hexagon: include default ioremap_nopost() implementation
>   ia64: include default ioremap_nopost() implementation
>   m32r: include default ioremap_nopost() implementation
>   m68k: include default ioremap_nopost() implementation
>   metag: include default ioremap_nopost() implementation
>   microblaze: include default ioremap_nopost() implementation
>   mips: include default ioremap_nopost() implementation
>   mn10300: include default ioremap_nopost() implementation
>   nios2: include default ioremap_nopost() implementation
>   openrisc: include default ioremap_nopost() implementation
>   parisc: include default ioremap_nopost() implementation
>   powerpc: include default ioremap_nopost() implementation
>   s390: include default ioremap_nopost() implementation
>   sh: include default ioremap_nopost() implementation
>   sparc: include default ioremap_nopost() implementation
>   tile: include default ioremap_nopost() implementation
>   unicore32: include default ioremap_nopost() implementation
>   x86: include default ioremap_nopost() implementation
>   xtensa: include default ioremap_nopost() implementation
>   arm64: implement ioremap_nopost() interface
>   arm: implement ioremap_nopost() interface
>   lib: fix Devres devm_ioremap_* offset parameter kerneldoc
> description
>   lib: implement Devres ioremap_nopost() interface
> 
>  Documentation/driver-model/devres.txt |  3 ++
>  arch/alpha/include/asm/io.h           |  1 +
>  arch/arc/include/asm/io.h             |  1 +
>  arch/arm/include/asm/io.h             |  9 ++++
>  arch/arm/mm/ioremap.c                 |  7 +++
>  arch/arm/mm/nommu.c                   |  9 ++++
>  arch/arm64/include/asm/io.h           | 12 +++++
>  arch/avr32/include/asm/io.h           |  1 +
>  arch/cris/include/asm/io.h            |  1 +
>  arch/frv/include/asm/io.h             |  1 +
>  arch/hexagon/include/asm/io.h         |  2 +
>  arch/ia64/include/asm/io.h            |  1 +
>  arch/m32r/include/asm/io.h            |  1 +
>  arch/m68k/include/asm/io.h            |  1 +
>  arch/metag/include/asm/io.h           |  2 +
>  arch/microblaze/include/asm/io.h      |  1 +
>  arch/mips/include/asm/io.h            |  1 +
>  arch/mn10300/include/asm/io.h         |  1 +
>  arch/nios2/include/asm/io.h           |  1 +
>  arch/openrisc/include/asm/io.h        |  2 +
>  arch/parisc/include/asm/io.h          |  1 +
>  arch/powerpc/include/asm/io.h         |  1 +
>  arch/s390/include/asm/io.h            |  1 +
>  arch/sh/include/asm/io.h              |  1 +
>  arch/sparc/include/asm/io.h           |  1 +
>  arch/tile/include/asm/io.h            |  1 +
>  arch/unicore32/include/asm/io.h       |  1 +
>  arch/x86/include/asm/io.h             |  1 +
>  arch/xtensa/include/asm/io.h          |  1 +
>  drivers/pci/pci.c                     |  4 +-
>  include/asm-generic/ioremap-nopost.h  |  9 ++++
>  include/asm-generic/pgtable.h         |  4 ++
>  include/linux/device.h                |  2 +
>  include/linux/io.h                    |  2 +
>  lib/devres.c                          | 84
> +++++++++++++++++++++++++++++++++--
>  35 files changed, 167 insertions(+), 5 deletions(-)
>  create mode 100644 include/asm-generic/ioremap-nopost.h
> 

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