From: Arnd Bergmann <arnd@arndb.de>
To: linux-arm-kernel@lists.infradead.org
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>,
stable@vger.kernel.org, linux-sunxi@googlegroups.com,
linux-mtd@lists.infradead.org,
Maxime Ripard <maxime.ripard@free-electrons.com>,
Brian Norris <computersforpeace@gmail.com>,
David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v4] mtd: nand: sunxi: fix OOB handling in ->write_xxx() functions
Date: Mon, 14 Sep 2015 14:36 +0200 [thread overview]
Message-ID: <3052942.HDd39OoZnN@wuerfel> (raw)
In-Reply-To: <3809181.WuS0af6Yyz@wuerfel>
On Monday 14 September 2015 13:49:12 Arnd Bergmann wrote:
> > > If all hardware can do 32-bit accesses here and the size is guaranteed to be a
> > > multiple of four bytes, you can probably improve performance by using a
> > > __raw_writel() loop there. Using __raw_writel() in general is almost always
> > > a bug, but here it actually makes sense. See also the powerpc implementation
> > > of _memcpy_toio().
> >
> > AFAICT, buffer passed to ->write_bu() are not necessarily aligned on
> > 32bits, so using writel here might require copying data in temporary
> > buffers :-/.
> >
> > Don't hesitate to point where I'm wrong ;-).
>
> Brian or Dwmw2 should be able to know for sure. I think it's definitely
> worth trying as the potential performance gains could be huge, if you
> replace
>
> for (p = start; p < start + length; data++, p++) {
> writeb(*data, p);
> wmb();
> }
>
> with
>
> for (p = start; p < start + length; data++, p+=4) {
> writel(*data, p);
> };
> wmb();
>
As Boris pointed out on IRC, we have an optimized version of
memcpy_toio on little-endian, which already does this. I'm not completely
sure why we don't use it for big-endian architectures as well.
Powerpc uses the same method on big-endian, but it's possible that
it does not do the right thing on one of the older platforms using
BE32 mode, or one that has a weird bus mode.
Arnd
WARNING: multiple messages have this Message-ID (diff)
From: arnd@arndb.de (Arnd Bergmann)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v4] mtd: nand: sunxi: fix OOB handling in ->write_xxx() functions
Date: Mon, 14 Sep 2015 14:36 +0200 [thread overview]
Message-ID: <3052942.HDd39OoZnN@wuerfel> (raw)
In-Reply-To: <3809181.WuS0af6Yyz@wuerfel>
On Monday 14 September 2015 13:49:12 Arnd Bergmann wrote:
> > > If all hardware can do 32-bit accesses here and the size is guaranteed to be a
> > > multiple of four bytes, you can probably improve performance by using a
> > > __raw_writel() loop there. Using __raw_writel() in general is almost always
> > > a bug, but here it actually makes sense. See also the powerpc implementation
> > > of _memcpy_toio().
> >
> > AFAICT, buffer passed to ->write_bu() are not necessarily aligned on
> > 32bits, so using writel here might require copying data in temporary
> > buffers :-/.
> >
> > Don't hesitate to point where I'm wrong ;-).
>
> Brian or Dwmw2 should be able to know for sure. I think it's definitely
> worth trying as the potential performance gains could be huge, if you
> replace
>
> for (p = start; p < start + length; data++, p++) {
> writeb(*data, p);
> wmb();
> }
>
> with
>
> for (p = start; p < start + length; data++, p+=4) {
> writel(*data, p);
> };
> wmb();
>
As Boris pointed out on IRC, we have an optimized version of
memcpy_toio on little-endian, which already does this. I'm not completely
sure why we don't use it for big-endian architectures as well.
Powerpc uses the same method on big-endian, but it's possible that
it does not do the right thing on one of the older platforms using
BE32 mode, or one that has a weird bus mode.
Arnd
next prev parent reply other threads:[~2015-09-14 12:36 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-14 8:41 [PATCH v4] mtd: nand: sunxi: fix OOB handling in ->write_xxx() functions Boris Brezillon
2015-09-14 8:41 ` Boris Brezillon
2015-09-14 8:59 ` Arnd Bergmann
2015-09-14 8:59 ` Arnd Bergmann
2015-09-14 9:41 ` Boris Brezillon
2015-09-14 9:41 ` Boris Brezillon
2015-09-14 11:49 ` Arnd Bergmann
2015-09-14 11:49 ` Arnd Bergmann
2015-09-14 12:36 ` Arnd Bergmann [this message]
2015-09-14 12:36 ` Arnd Bergmann
2015-09-14 17:02 ` Brian Norris
2015-09-14 17:02 ` Brian Norris
2015-09-21 20:43 ` Brian Norris
2015-09-21 20:43 ` Brian Norris
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