From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2] arm64: pci: add support for pci_mmap_page_range
Date: Mon, 20 Mar 2017 13:21:32 +0000 [thread overview]
Message-ID: <20170320132132.GN17263@arm.com> (raw)
In-Reply-To: <1489666647.4195.238.camel@infradead.org>
On Thu, Mar 16, 2017 at 12:17:27PM +0000, David Woodhouse wrote:
> On Fri, 2016-04-15 at 14:09 +0100, Will Deacon wrote:
> >
> > > +?????if (write_combine)
> > > +?????????????vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> > > +?????else
> > > +?????????????vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> >
> > For consistency with ioremap, this should be pgprot_device.
>
> What's the difference?
The different between ioremap (which used pgprot_device) and a mapping
created using pgprot_noncached is that the former allows for early
acknowledgement of writes (e.g. at a bridge). See this recent series from
Lorenzo that is also trying to clean this up:
http://lkml.kernel.org/r/20170227151436.18698-1-lorenzo.pieralisi at arm.com
> I note that VFIO is using pgprot_noncached() too, in vfio_pci_mmap() ?
> where it open-codes an entirely arch-agnostic version of
> pci_mmap_page_range() all for itself. Should that be changed to
> pgprot_device() too?
I think so. At least, on arm64, pgprot_noncached is only really needed
for PCI config space and "I don't know that this is, but I'm going to map
it anyway" regions in /dev/mem.
> Let me see if I can get this straight...
>
> We have the legacy interface through /proc/bus/pci, where the user
> passes a "user-visible" bus address not necessarily (on platforms with
> HAVE_PCI_RESOURCE_TO_USER) a host physical address.
>
> The arch-specific pci_mmap_page_range() exists to work around that
> translation, on the two platforms which need it. It *also* has (on
> about three platforms) support for a write-combining mapping.
>
> The sysfs interface theough /sys/bus/pci/devices/*/resource* probably
> doesn't need to use pci_mmap_page_range() at all, *except* for the
> 'resourceX_wc' variant which has write-combining support.
>
> How about we do the following (probably not in this order):
> ?? Kill pci_mmap_page_range() entirely.
> ?? Implement a generic version which has (arch-assisted) WC support
> ? ?but no knowledge of the horrid pci_resource_to_user() mapping.
> ?? Require pci_user_to_resource() to be provided by platforms with
> ? ?HAVE_ARCH_PCI_RESOURCE_TO_USER, and call that from *generic* code,
> ? ?for the legacy procfs interface, before invoking the generic
> ? ?replacement for pci_mmap_page_range().
>
> (Yes, we still need to support mmap of I/O resources on... is it only
> powerpc? And there are a few inconsistencies, like powerpc forcing WC
> even on the sysfs files that *don't* have _wc in their name, that
> probably want to be cleaned up as we consolidate...)
Happy to review patches :)
Will
prev parent reply other threads:[~2017-03-20 13:21 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-13 21:10 [PATCH v2] arm64: pci: add support for pci_mmap_page_range Jerin Jacob
2016-04-15 13:09 ` Will Deacon
2016-04-15 18:45 ` Arnd Bergmann
2016-04-18 14:01 ` Jerin Jacob
2016-04-18 14:15 ` Arnd Bergmann
2016-04-18 14:53 ` Jerin Jacob
2016-04-18 15:00 ` Arnd Bergmann
2016-04-18 15:21 ` Jerin Jacob
2016-04-18 15:31 ` Arnd Bergmann
2016-04-18 15:40 ` Will Deacon
2016-04-18 17:45 ` Jerin Jacob
2016-04-18 17:46 ` Arnd Bergmann
2017-03-15 21:01 ` David Woodhouse
2017-03-20 13:18 ` Will Deacon
2017-03-20 14:07 ` David Woodhouse
2016-04-18 13:43 ` Jerin Jacob
2017-03-16 12:17 ` David Woodhouse
2017-03-20 13:21 ` Will Deacon [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170320132132.GN17263@arm.com \
--to=will.deacon@arm$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox