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

[Andy Lutomirski]

On Fri, Aug 9, 2013 at 11:47 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> On Fri, Aug 9, 2013 at 8:39 PM, Andy Lutomirski <luto at amacapital.net> wrote:
>> 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.
>
> Oh that kind of confusion. The maps code here is for old userspace
> drivers, I have some patches in the queue that will disable it
> properly for kms drivers. So it should never happen that both the kms
> driver and the maps code in the drm core set up a mtrr mapping. And if
> it happens someone is doing something really nasty, and that hole will
> soon be plugged.

In that case, I'm convinced.  In case you care:

Acked-by: Andy Lutomirski <luto at amacapital.net>

--Andy

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



-- 
Andy Lutomirski
AMA Capital Management, LLC