linux-kernel - Re: [PATCH 2/7] drm (ast, cirrus, mgag200, nouveau, savage, vmwgfx): Rework drm_mtrr

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Message-ID: <CALCETrXVN_b2T93kMc=342h+1++mjucHS0btir1UZOa3CS+R-g@mail.gmail.com>
Date:	Sat, 4 May 2013 10:48:33 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-fbdev@...r.kernel.org
Subject: Re: [PATCH 2/7] drm (ast, cirrus, mgag200, nouveau, savage, vmwgfx):
 Rework drm_mtrr_{add, del}

On Sat, May 4, 2013 at 10:45 AM, Daniel Vetter <daniel@...ll.ch> wrote:
> On Fri, May 03, 2013 at 04:00:30PM -0700, Andy Lutomirski wrote:
>> This replaces drm_mtrr_{add,del} with drm_mtrr_{add,del}_wc.  The
>> interface is simplified (because the base and size parameters to
>> drm_mtrr_del never did anything) and it uses
>> mtrr_{add,del}_wc_if_needed to avoid allocating MTRRs on systems
>> that don't need them.
>>
>> Signed-off-by: Andy Lutomirski <luto@...capital.net>
>> ---
>
>
> Tbh I'm not a big fan of the drm_ indirection. Historically that was
> useful as an OS abstraction layer so that the same drivers could be used
> unchanged on Linux and the *BSD. But those days are long gone and drm
> drivers are now proper Linux drivers, and generally OS HALs seem to be
> frowned upon.
>
> Is there another reason than just being consistent with the historic stuff
> here? If we need dummy functions for !CONFIG_MTRR I think those should
> simply be in the core.


I admit to a bit of cargo-culting.  There was a layer of indirection,
so I kept it.  I'll just call mtrr_add/del_wc_if_needed directly in v2
(I added those functions in patch 1 of this series).

I'd assume you're okay with skipping mtrr addition if PAT is available
since i915 already does it :)  (Although the current logic is buggy --
cpu_has_pat is the wrong flag to check -- I think pat_enabled is
better.)

Note to self: I should remove #include <asm/pat.h> in i915_dma.c in v2.

--Andy
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