Synchronization between a crtc mode_set and page_flip?

[Rob Clark]

On Wed, Apr 2, 2014 at 5:52 AM, Archit Taneja <archit at ti.com> wrote:
> Hi,
>
> I was trying to figure out how we are supposed to manage synchronization
> between a mode_set and a page_flip called on a crtc.
>
> Say, if a mode_set is immediately followed by a page_flip. The driver can't
> process the page_flip straight away since the hardware is still completing
> the mode_set.

I guess setcrtc is expected to be synchronous(ish).. so a lot of
userspace won't expect the first pageflip to fail with -EBUSY.

BR,
-R

> What is the driver supposed to do? Should it return -EBUSY? Or should it
> somehow queue the page_flip task internally?
>
> A lot of libdrm applications seem to call mode_set, and call a page_flip
> soon after it. They tend to bail out if page_flip returns an error, they
> don't try to do another page_flip if it fails the first time. Is this okay
> behaviour?
>
> Thanks,
> Archit
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