[PATCH 17/25] drm: rip out drm_core_has_MTRR checks

[Andy Lutomirski]

On Fri, Aug 9, 2013 at 11:36 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> On Fri, Aug 9, 2013 at 8:12 PM, Andy Lutomirski <luto at amacapital.net> wrote:
>> On Thu, Aug 8, 2013 at 6:41 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>>> The new arch_phys_wc_add/del functions do the right thing both with
>>> and without MTRR support in the kernel. So we can drop these
>>> additional checks.
>>
>> If any of the new arch_phys_wc_add calls are reachable and if the
>> driver calls arch_phys_wc_add itself, then the lack of refcounting on
>> non-PAT systems may cause a problem.  (I don't understand the drm
>> stuff well enough to know whether that can actually happen.)
>
> This is only about compile-time options really. Somehow drm had the
> idea to use these check functions instead of #ifdef plus dummy static
> inline noop functions. David Herrmann just did the same patch for the
> agp stuff. So refcounting is of no concern here.

I feel like I'm missing something obvious here.  On nouveau, prior to
this patch, the drm maps code would not touch mtrrs.  Now it will.
Nouveau already calls arch_phys_wc_add, so if that maps code is
reached on the same resource, then there could be refcounting issues.

--Andy

> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch



-- 
Andy Lutomirski
AMA Capital Management, LLC