From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Dave Airlie <airlied@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: vga and 64-bit memcpy's
Date: Fri, 12 Sep 2014 11:26:19 +0100 [thread overview]
Message-ID: <20140912112619.50d3b651@www.etchedpixels.co.uk> (raw)
In-Reply-To: <CAPM=9tyZF2S7PJcLyc=KH_NBFXju8UwvMBOF_MocNK8pPVXDYw@mail.gmail.com>
On Fri, 12 Sep 2014 13:57:20 +1000
Dave Airlie <airlied@gmail.com> wrote:
> Got an bug report from someone using a silicon motion video card in
> VGA mode about corruption that they tracked down to 64-bit memory
> operations not being supported by the video card, it appears that we
> probably shouldn't be using > 32-bit copies on VGA memory.
VGA memory is write combining usually so the answer in general would be
no. You may also find its a combination of bridge and card and one or the
other is somehow out of spec.
> The include/linux/vt_buffer.h defaults scr_memcpyw defaults to using
> memcpy, which on 64-bit x86 machines ends up as rep movsq. Is there
> any way to make this use a 32-bit memcpy instead?
Please don't - you'll reduce performance for everyone else with saner
video cards.
Alan
next prev parent reply other threads:[~2014-09-12 10:26 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-12 3:57 Dave Airlie
2014-09-12 10:26 ` Alan Cox [this message]
2014-09-12 10:48 ` Dave Airlie
2014-09-12 15:11 ` Linus Torvalds
2014-10-21 4:30 ` Dave Airlie
2014-10-21 19:53 ` Linus Torvalds
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