[Intel-gfx] [PATCH v3 2/4] drm/i915: Wait for pending flips in intel_pipe_set_base()

[Daniel Vetter]

On Fri, Nov 30, 2012 at 3:01 PM, Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
> I had another look at this, and I think you're aiming for something other
> than what this patch is trying to do.

Oh, I know that I'm trying to volunteer you to do a bit more ... it's
why I'm the bastard maintainer ;-)

> The thing is that we are holding struct_mutex while waiting for pending
> flips here, so we just need to get out asap to allow the reset work do
> its thing.

Hm, I didn't notice that we're holding the struct_mutex there, so I
guess we need to indeed bail out. Or rework the finsh_fb vs. gpu hang
logic to not require the struct_mutex in finish_fb ...

> Completing pending page flips when a reset occurs is separate issue.
> This code never did any of that, and I don't see why it should. We
> would need to complete them anyway regardless of whether anyone is
> currently waiting for them.

Yeah, that's my idea, but I haven't though through the details (see my
ignorance with locking details above ...).

> Perhaps we can just call intel_finish_page_flip() from the reset
> code and call it a day. I suppose doing that could end up unpinning
> the current scanout buffer in case the display registers were never
> written with the new values. One solution for that would be to always
> do a set_base() after a reset. That would make sure we end up showing
> the latest buffer at least, although the contents could be total
> garbage.

Hm, I think first we should aim to no longer hang either the kernel or
leave stuck userspace (since the drm_event never shows up) behind. Atm
a gpu hang is allowed to corrupt pretty much everything. Later on,
when we successfully avoid the hung kernel/userspace problems we can
worry about making it look decent. Judging by how long it took to get
basic reset working somewhat okish, it'll take a while. And we need
some form of testcase to exercise the code.

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