linux-kernel - Re: [PATCH] mtd: phram: Map RAM using memremap instead of ioremap

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Message-ID: <Youn9AmqY6/EExDw@ntb.petris.klfree.czf>
Date:   Mon, 23 May 2022 17:27:48 +0200
From:   Petr Malat <oss@...at.biz>
To:     David Laight <David.Laight@...lab.com>
Cc:     "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        Joern Engel <joern@...ybastard.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] mtd: phram: Map RAM using memremap instead of ioremap

Hi!

On Mon, May 23, 2022 at 02:51:41PM +0000, David Laight wrote:
> From: Petr Malat
> > Sent: 23 May 2022 15:28
> > 
> > One can't use memcpy on memory obtained by ioremap, because IO memory
> > may have different alignment and size access restriction than the system
> > memory. Use memremap as phram driver operates on RAM.
> 
> Does that actually help?
> The memcpy() is still likely to issue unaligned accesses
> that the hardware can't handle.

Yes, it solves the issue. Memcpy can cause unaligned access only on
platforms, which can handle it. And on ARM64 it's handled only for
RAM and not for a device memory (__pgprot(PROT_DEVICE_*)).
  Petr