From: catalin.marinas@arm•com (Catalin Marinas)
To: linux-arm-kernel@lists•infradead.org
Subject: memcpy alignment for DEVICE_nGnRnE
Date: Wed, 9 Apr 2014 09:17:05 +0100 [thread overview]
Message-ID: <20140409081705.GB13737@arm.com> (raw)
In-Reply-To: <20140408233937.GA2100@codeaurora.org>
On Wed, Apr 09, 2014 at 12:39:37AM +0100, Michael Bohan wrote:
> On Tue, Apr 08, 2014 at 12:49:49PM +0100, Catalin Marinas wrote:
> > On Tue, Apr 08, 2014 at 01:35:47AM +0100, Michael Bohan wrote:
> > > How should we handle Device Memory with copy_from_user / copy_to_user?
> > > Should we follow the same scheme and create
> > > copy_from_user_io / copy_to_user_io, or rather enforce that the stock
> > > routines handle alignment?
> >
> > We have generic copy_from_user_toio() and copy_to_user_fromio(). Are
> > these what you need? As with the memcpy_(to|from)io, they can be further
> > optimised.
>
> It seems these existing routines are in sound. Were you thinking
> the right approach would be to move them out of sound and make
> them per-arch defined?
If you have a use-case outside of the sound subsystem, they can be made
more generic.
> What about the other two use cases: copy_from_user_fromio and
> copy_to_user_toio? Are those reasonable to add? These two APIs
> would cover the use case I had in mind.
What's the use case for these?
> Then what about the strange but possible use case where both the
> source and destination pointers are iomem? This same question
> applies for memcpy_fromio / memcpy_toio as well.
You can come up with many combinations but we first need to see a real
use of them, eliminate the alternatives and only then look at adding new
API.
> The implementations of copy_from_user_toio and
> copy_to_user_fromio are currently doing a second copy, so that
> seems bad for performance. We'd probably want to improve these as
> well if others are in agreement.
Yes, as I said they are not optimised (but good enough as a start).
--
Catalin
prev parent reply other threads:[~2014-04-09 8:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <53072343.4080505@marvell.com>
2014-02-21 10:53 ` memcpy alignment for DEVICE_nGnRnE Catalin Marinas
2014-04-08 0:35 ` Michael Bohan
2014-04-08 11:49 ` Catalin Marinas
2014-04-08 23:39 ` Michael Bohan
2014-04-09 8:17 ` Catalin Marinas [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=20140409081705.GB13737@arm.com \
--to=catalin.marinas@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