Nouveau - Oct 2024 - [PATCH 2/2] drm: Move crtc->{x, y, mode, enabled} to legacy sub-structure

On Thu, Oct 03, 2024 at 02:38:35PM +0200, Louis Chauvet
wrote:
> Le 02/10/24 - 21:22, Ville Syrjala a ?crit :
> > From: Ville Syrj?l? <ville.syrjala at linux.intel.com>
> > 
> > Atomic drivers shouldn't be using the legacy state stored
> > directly under drm_crtc. Move that junk into a 'legacy' sub
> > structure to highlight the offenders, of which there are
> > quite a few unfortunately.
> 
> Hi,
> 
> Do we need to do something particular in an atomic driver except using
> state content?
> 
> I proposed some modifications for VKMS bellow. If you think this is good,
> I can send a patch to avoid being an offender :-) I just tested it, and it
> seems to work.
> 
> > I'm hoping we could get all these fixed and then declare
> > the legacy state off limits for atomic drivers (which is
> > what did long ago for plane->fb/etc). And maybe eventually
> > turn crtc->legacy into a pointer and only allocate it on
> > legacy drivers.
> > 
> > TODO: hwmode should probably go there too but it probably
> >       needs a closer look, maybe other stuff too...
> 
> [...]
> 
> > diff --git a/drivers/gpu/drm/vkms/vkms_composer.c
b/drivers/gpu/drm/vkms/vkms_composer.c
> > index 57a5769fc994..a7f8b1da6e85 100644
> > --- a/drivers/gpu/drm/vkms/vkms_composer.c
> > +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> > @@ -187,7 +187,7 @@ static void blend(struct vkms_writeback_job *wb,
> >  
> >  	const struct pixel_argb_u16 background_color = { .a = 0xffff };
> >  
> > -	size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;
> > +	size_t crtc_y_limit =
crtc_state->base.crtc->legacy.mode.vdisplay;
> 
> 	size_t crtc_y_limit = crtc_state->base.mode.vdisplay;
> 
> >  	/*
> >  	 * The planes are composed line-by-line to avoid heavy memory usage.
It is a necessary
> > @@ -270,7 +270,7 @@ static int compose_active_planes(struct
vkms_writeback_job *active_wb,
> >  	if (WARN_ON(check_format_funcs(crtc_state, active_wb)))
> >  		return -EINVAL;
> >  
> > -	line_width = crtc_state->base.crtc->mode.hdisplay;
> > +	line_width = crtc_state->base.crtc->legacy.mode.hdisplay;
> 
> 	line_width = crtc_state->base.mode.hdisplay;
> 
> >  	stage_buffer.n_pixels = line_width;
> >  	output_buffer.n_pixels = line_width;
> >  
> > diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c
b/drivers/gpu/drm/vkms/vkms_crtc.c
> > index a40295c18b48..780681ea77e4 100644
> > --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> > +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> > @@ -64,7 +64,7 @@ static int vkms_enable_vblank(struct drm_crtc *crtc)
> >  	struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc);
> >  	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> >  
> > -	drm_calc_timestamping_constants(crtc, &crtc->mode);
> > +	drm_calc_timestamping_constants(crtc, &crtc->legacy.mode);
> 
> 	drm_calc_timestamping_constants(crtc, &crtc->state->mode);
This one doesn't look safe. You want to call that during your atomic
commit already.

The rest look reasonable.
> 
> >  	hrtimer_init(&out->vblank_hrtimer, CLOCK_MONOTONIC,
HRTIMER_MODE_REL);
> >  	out->vblank_hrtimer.function = &vkms_vblank_simulate;
> > diff --git a/drivers/gpu/drm/vkms/vkms_writeback.c
b/drivers/gpu/drm/vkms/vkms_writeback.c
> > index bc724cbd5e3a..27164cddb94d 100644
> > --- a/drivers/gpu/drm/vkms/vkms_writeback.c
> > +++ b/drivers/gpu/drm/vkms/vkms_writeback.c
> > @@ -131,8 +131,8 @@ static void vkms_wb_atomic_commit(struct
drm_connector *conn,
> >  	struct drm_connector_state *conn_state = wb_conn->base.state;
> >  	struct vkms_crtc_state *crtc_state = output->composer_state;
> >  	struct drm_framebuffer *fb =
connector_state->writeback_job->fb;
> > -	u16 crtc_height = crtc_state->base.crtc->mode.vdisplay;
> > -	u16 crtc_width = crtc_state->base.crtc->mode.hdisplay;
> > +	u16 crtc_height = crtc_state->base.crtc->legacy.mode.vdisplay;
> > +	u16 crtc_width = crtc_state->base.crtc->legacy.mode.hdisplay;
> 
> 	u16 crtc_height = crtc_state->base.mode.vdisplay;
> 	u16 crtc_width = crtc_state->base.mode.hdisplay;
> 
> >  	struct vkms_writeback_job *active_wb;
> >  	struct vkms_frame_info *wb_frame_info;
> >  	u32 wb_format = fb->format->format;
> 
> [...]
> 
> -- 
> Louis Chauvet, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
-- 
Ville Syrj?l?
Intel

> > > diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c
b/drivers/gpu/drm/vkms/vkms_crtc.c
> > > index a40295c18b48..780681ea77e4 100644
> > > --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> > > +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> > > @@ -64,7 +64,7 @@ static int vkms_enable_vblank(struct drm_crtc
*crtc)
> > >  	struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc);
> > >  	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> > >  
> > > -	drm_calc_timestamping_constants(crtc, &crtc->mode);
> > > +	drm_calc_timestamping_constants(crtc,
&crtc->legacy.mode);
> > 
> > 	drm_calc_timestamping_constants(crtc, &crtc->state->mode);
> 
> This one doesn't look safe. You want to call that during your atomic
> commit already.
> 
This was already not safe with the previous implementation? Or it is only 
unsafe because now I use state->mode instead of legacy.mode?

After inspecting the code, I think I don't need to call it as:

In `vkms_atomic_commit_tail` (used in 
`@vkms_mode_config_helpers.atomic_commit_tail`), we call 
`drm_atomic_helper_commit_modeset_disables`, which call 
`drm_atomic_helper_calc_timestamping_constants` which call 
`drm_calc_timestamping_constants` for every CRTC.

I tested kms_vblank, all of them are SUCCESS/SKIP, do you know other tests 
that can trigger bugs?

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com