[Intel-gfx] [PATCH] drm/i915: Also perform gpu reset under execlist mode.

[Daniel Vetter]

On Thu, Jun 25, 2015 at 09:13:13AM +0100, Chris Wilson wrote:
> On Thu, Jun 25, 2015 at 10:40:15PM +0800, bing.niu at intel.com wrote:
> > From: "Niu,Bing" <bing.niu at intel.com>
> > 
> > It is found that i915 will not reset gpu under execlist mode when
> > unload module. that will lead to some issues when unload/load module
> > with different submission mode. e.g. from execlist mode to ring
> > buffer mode via loading/unloading i915. Because HW is not in a reset
> > state and registers are not clean under such condition.
> 
> Now the reason we have the reset there is to disable writes to the power
> context after the memory is released. Your complaint above can easily be
> read as the driver is unable to correctly initialisae itself from a
> random GPU state, which is a fault in driver initialisation.
> 
> Have you observed stray memory writes from the GPU after the module is
> unloaded? If not, this would seem to be just a band-aid.

I think as long as we don't have any bios out there enabling execlist
already it's better to try to leave the gpu behind in a state consistent
what we're seeing from real firmware. Otherwise we just have complexity
for no reason.

Similar example is that we kill all outputs since our pte setup doesn't
math the bios one (and yeah I think there too it'd be good to fill out the
gtt with stolen ptes). Hence this patch makes sense for me.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch