linux-kernel - Re: [PATCH v4] mtd: phram: Allow cached mappings

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Message-Id: <20220512152701.244667-1-miquel.raynal@bootlin.com>
Date:   Thu, 12 May 2022 17:27:01 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Joern Engel <joern@...ybastard.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>
Cc:     kernel@...s.com, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] mtd: phram: Allow cached mappings

On Tue, 2022-05-10 at 15:18:22 UTC, Vincent Whitchurch wrote:
> Currently phram always uses ioremap(), but this is unnecessary when
> normal memory is used.  If the reserved-memory node does not specify the
> no-map property, indicating it should be mapped as system RAM and
> ioremap() cannot be used on it, use a cached mapping using
> memremap(MEMREMAP_WB) instead.
> 
> On one of my systems this improves read performance by ~70%.
> 
> (Note that this driver has always used normal memcpy/memset functions on
> memory obtained from ioremap(), which sparse doesn't like.  There is no
> memremap() variant which maps exactly to ioremap() on all architectures,
> so that behaviour of the driver is not changed to avoid affecting
> existing users, but the sparse warnings are suppressed in the moved code
> with __force.)
> 
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/next, thanks.

Miquel