On 03/18, Chris Wilson wrote:
> Quoting Rodrigo Siqueira (2019-03-18 21:35:44)
> > On 03/18, Ville Syrjälä wrote:
> > > On Sat, Mar 16, 2019 at 11:00:23AM -0300, Rodrigo Siqueira wrote:
> > > > The kms_flip test relies on VBlank support, and this situation may
> > > > exclude some virtual drivers to take advantage of this set of tests.
> > > > This commit adds a mechanism that checks if a module has VBlank. If the
> > > > target module has VBlank support, kms_flip will run all the VBlank
> > > > tests; otherwise, the VBlank tests will be skipped. Additionally, this
> > > > commit improves the test coverage by checks if the function
> > > > drmWaitVBlank() returns EOPNOTSUPP (i.e., no VBlank support).
> > > >
> > > > V4: Replace DRM_VBLANK_ABSOLUTE by DRM_VBLANK_RELATIVE and
> > > > DRM_VBLANK_NEXTONMISS
> > > >
> > > > V3: Add documentation (Daniel Vetter)
> > > >
> > > > V2: Add new branch coverage to check if VBlank is enabled or not and
> > > > update commit message
> > > >
> > > > V1: Chris Wilson
> > > > - Change function name from igt_there_is_vblank to kms_has_vblank
> > > > - Move vblank function check from igt_aux to igt_kms
> > > > - Utilizes memset in dummy_vbl variable
> > > > - Directly return the result of drmWaitVBlank()
> > > >
> > > > Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>
> > > > ---
> > > > lib/igt_kms.c | 20 ++++++++++++++++++++
> > > > lib/igt_kms.h | 2 ++
> > > > tests/kms_flip.c | 22 ++++++++++++++++++++++
> > > > 3 files changed, 44 insertions(+)
> > > >
> > > > diff --git a/lib/igt_kms.c b/lib/igt_kms.c
> > > > index e1eacc1e..1d2d7188 100644
> > > > --- a/lib/igt_kms.c
> > > > +++ b/lib/igt_kms.c
> > > > @@ -1655,6 +1655,26 @@ void igt_assert_plane_visible(int fd, enum pipe pipe, bool visibility)
> > > > igt_assert_eq(visible, visibility);
> > > > }
> > > >
> > > > +/**
> > > > + * kms_has_vblank:
> > > > + * @fd: DRM fd
> > > > + *
> > > > + * Get the VBlank errno after an attempt to call drmWaitVBlank(). This
> > > > + * function is useful for checking if a driver has support or not for VBlank.
> > > > + *
> > > > + * Returns: true if target driver has VBlank support, otherwise return false.
> > > > + */
> > > > +bool kms_has_vblank(int fd)
> > > > +{
> > > > + drmVBlank dummy_vbl;
> > > > +
> > > > + memset(&dummy_vbl, 0, sizeof(drmVBlank));
> > > > + dummy_vbl.request.type = DRM_VBLANK_RELATIVE | DRM_VBLANK_NEXTONMISS;
> > >
> > > Why the NEXTONMISS?
> >
> > I added this flag because I was suspecting that in case of any problem
> > during the kms_has_vblank() execution the flag NEXTONMISS will wait for
> > the next VBlank and avoid to generate problems in the subsequent tests.
>
> That is true, and a valid use for using NEXTONMISS if you want to align
> your code to the start of a vblank to avoid overrunning into the next
> vblank.
>
> However, that is not the purpose of kms_has_vblank()! Whose only purpose
> is answer the question of whether the device has vblank support, and so
> should be as quick and simple as possible, so the trivial query of the
> current vblank counter.
Nice! Thanks for your answer.
So, I suppose that use DRM_VBLANK_RELATIVE is enough for this case,
right?
> -Chris
--
Rodrigo Siqueira
https://siqueira.tech
Graduate Student
Department of Computer Science
University of São Paulo
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