linux-kernel - Re: [PATCH 3/7] drm: Update drm_addmap and drm

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Message-ID: <CALCETrVe=JSPB=x79e1fAK=DrMgo7_Liagihib9quJDJ0N670Q@mail.gmail.com>
Date:	Mon, 6 May 2013 14:22:37 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-fbdev@...r.kernel.org
Cc:	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH 3/7] drm: Update drm_addmap and drm_mmap to use PAT WC
 instead of MTRRs

On Fri, May 3, 2013 at 4:00 PM, Andy Lutomirski <luto@...capital.net> wrote:
> Signed-off-by: Andy Lutomirski <luto@...capital.net>
> ---
>
> This needs careful review.  I don't really know what this code does, nor
> do I have the hardware.  (I don't understand AGP and the associated
> caching implications.)

This patch is wrong (I didn't update the matching mtrr_del), and I'm
reworking this whole series.  But I may need some help on this one:
why is the mtrr handle of a map (whatever a map is) exported to
userspace via the ADD_MAP and GET_MAP ioctls?  What (if anything) is
userspace supposed to do with it?  Do I need to return a valid MTRR
register number?  Is there any userspace code at all that sets
_DRM_WRITE_COMBINING in DRM_IOCTL_ADD_MAP with appropriate alignment
and needs the MTRR, for which the drm driver doesn't already add the
MTRR?

--Andy
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