linux-kernel - Re: [PATCH v11 04/60] sparc/PCI: Use correct offset for bus address to resource

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Date:	Tue, 3 May 2016 20:25:31 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	David Miller <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Wei Yang <weiyang@...ux.vnet.ibm.com>, TJ <linux@....tj>,
	Yijing Wang <wangyijing@...wei.com>,
	Khalid Aziz <khalid.aziz@...cle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v11 04/60] sparc/PCI: Use correct offset for bus address
 to resource

On Wed, May 04, 2016 at 10:37:40AM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2016-05-03 at 15:52 -0700, Yinghai Lu wrote:
> > BenH and DavidM,
> > Are you ok to let /proc/bus/pci/devices to expose resource value
> > instead of
> > BAR value?
> > powerpc already expose MMIO as resource value, but still keep IO as
> > BAR value?
> > 
> > Or can we just dump /proc/bus/pci support from now?
> 
> The problem tends to be old Xserver expectations...
> 
> That stuff has been a can of worms over the years and we did things in
> the kernel to work around X limitations. I'm not that keen on touching
> /proc at all in that regard. Leave it there do what it does today, it's
> a user visible ABI, don't change it.

I did not propose changing any user-visible ABI.  To recap what I did
propose:

  - The sysfs path uses offsets between 0 and BAR size on all arches.
    It uses pci_resource_to_user() today, but I think it should not.

  - The procfs path uses offsets of resource values (CPU physical
    addresses) on most architectures, but uses something else, e.g.,
    BAR values, on others.  pci_resource_to_user() does this
    translation.  The procfs path does not use pci_resource_to_user()
    today, but I think it should.

  - This implies that pci_mmap_page_range() should deal with resource
    values (CPU physical addresses), and proc_bus_pci_mmap() should do
    any necessary arch-specific translation from BAR values to
    resource values.