[Intel-gfx] [PATCH v4 02/38] drm/i915: Explicit power enable during deferred context initialisation

[John Harrison]

On 12/01/2016 11:28, Chris Wilson wrote:
> On Tue, Jan 12, 2016 at 11:11:20AM +0000, John Harrison wrote:
>> On 12/01/2016 00:20, Chris Wilson wrote:
>>> On Mon, Jan 11, 2016 at 06:42:31PM +0000, John.C.Harrison at Intel.com wrote:
>>>> From: John Harrison <John.C.Harrison at Intel.com>
>>>>
>>>> A later patch in this series re-organises the batch buffer submission
>>>> code. Part of that is to reduce the scope of a pm_get/put pair.
>>>> Specifically, they previously wrapped the entire submission path from
>>>> the very start to the very end, now they only wrap the actual hardware
>>>> submission part in the back half.
>>> However, as you haven't fixed the ordering issue that requires rpm_get
>>> before struct_mutex, this is broken.
>> Why does 'intel_runtime_pm_get' require the struct mutex to be held?
>> It has certainly not complained at me about trying to do stuff
>> without it.
> Because it depends upon the struct_mutex and rpm doesn't have sufficient
> lockdep integration to be able to warn about using rpm from the
> incorrect contexts.
Where? What does the 'pm_runtime_get_sync' call turn into? There are 
already other places in the driver which call intel_runtime_pm_get() 
immediately after grabbing the mutex lock. Also, the description comment 
for _pm_get() does not mention anything about mutexes at all.

> -Chris
>