On Sat, Oct 22, 2016 at 10:47:25AM +0200, Daniel Vetter wrote:
> On Fri, Oct 21, 2016 at 04:45:39PM -0700, Manasi Navare wrote:
> > This function provides a way for the driver to redo a
> > modeset on the current mode and retry the link training
> > at a lower link rate/lane count/bpp. This will get called
> > incase the link training fails during the current modeset.
> >
> > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
> > Signed-off-by: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/drm_atomic_helper.c | 58 +++++++++++++++++++++++++++++++++++++
> > include/drm/drm_atomic_helper.h | 1 +
> > 2 files changed, 59 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index f936276..0c1614e 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -2895,6 +2895,64 @@ int drm_atomic_helper_connector_dpms(struct drm_connector *connector,
> > EXPORT_SYMBOL(drm_atomic_helper_connector_dpms);
> >
> > /**
> > + * drm_atomic_helper_connector_modeset - Force a modeset on a connector
> > + * @connector: DRM connector
> > + *
> > + * Provides a way to redo a modeset with the current mode so that it can
> > + * drop the bpp, link rate/lane count and retry the link training.
> > + *
> > + * Returns:
> > + * Returns 0 on success, negative errno numbers on failure.
> > + */
> > +int
> > +drm_atomic_helper_connector_modeset(struct drm_connector *connector)
> > +{
> > + struct drm_device *dev = connector->dev;
> > + struct drm_modeset_acquire_ctx ctx;
> > + struct drm_atomic_state *state;
> > + struct drm_connector_state *connector_state;
> > + struct drm_crtc_state *crtc_state;
> > + int ret = 0;
> > +
> > + drm_modeset_acquire_init(&ctx, 0);
> > + state = drm_atomic_state_alloc(dev);
> > + if (!state) {
> > + ret = -ENOMEM;
> > + goto fail;
> > + }
> > + state->acquire_ctx = &ctx;
> > +retry:
> > + ret = 0;
> > + connector_state = drm_atomic_get_connector_state(state, connector);
> > + if (IS_ERR(connector_state)) {
> > + ret = PTR_ERR(connector_state);
> > + goto fail;
> > + }
> > + if (!connector_state->crtc)
> > + goto fail;
> > +
> > + crtc_state = drm_atomic_get_existing_crtc_state(state,
> > + connector_state->crtc);
> > + crtc_state->connectors_changed = true;
>
> This line here only works if the driver uses the helpers for checking and
> commit, and when it doesn't overwrite connectors_changed. I think the
> kerneldoc should mention this.
>
> The other issue: You cannot call this from modeset code itself because of
> recursion. I think this also must be mentioned.
And if this indeed does a modeset then we have again the same issue as
with upfront link training when the pipe is supposed to be on: Userspace
can observe the kernel playing tricks because the vblank support will be
temporarily disabled.
Not sure how to best fix this, but might be good to grab the crtc->mutex
in the vblank code for stuff like this.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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