linux-kernel - Re: [PATCH] parisc: Remove memcpy

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Message-Id: <543bd0f6-b25d-48b4-8039-496b8ddd10ce@app.fastmail.com>
Date: Fri, 31 Jan 2025 08:28:33 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Julian Vetter" <julian@...er-limits.org>,
 "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
 "Helge Deller" <deller@....de>
Cc: linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] parisc: Remove memcpy_fromio

On Thu, Jan 30, 2025, at 14:48, Julian Vetter wrote:
> Fully migrate parisc to the IO functions from lib/iomem_copy.c. In a
> recent patch the functions memset_io and memcpy_toio were removed, but
> the memcpy_fromio was kept, because for very short sequences it does
> half word accesses, whereas the functions in lib/iomem_copy.c do byte
> accesses until the memory is naturally aligned and then do machine word
> accesses. But I don't think the single half-word access merits keeping
> the arch specific implementation, so, remove it as well.
>
> Signed-off-by: Julian Vetter <julian@...er-limits.org>

Acked-by: Arnd Bergmann <arnd@...db.de>

This one looks fairly obvious. It might be nice to also
clean up the {in,out}s{b,w,l} helper functions in the same
file, but I don't understand why those are special
in the first place.

Those functions have been unchanged since before the git
history and there are some comments that I don't find helpful.
One thing they do is to deal with unaligned memory buffers,
which the generic ones don't, but that could be easily added
using get_unaligned/put_unaligned, expecting the compiler
to optimize the memory side of the transfer.

     Arnd