Re: [PATCH] drm/vkms: add module parameter to set background color

[Maíra Canal <mcanal@xxxxxxxxxx>]

On 4/6/23 14:28, Daniel Vetter wrote:
> On Thu, 6 Apr 2023 at 19:20, Maíra Canal <mcanal@xxxxxxxxxx> wrote:
> > After commit 8ba1648567e2 ("drm: vkms: Refactor the plane composer to
> > accept new formats") the composition is no longer performed on top of
> > the primary plane, but instead on top of the CRTC, which means that
> > now we have a background.
> >
> > This opens to the possibility of coloring the background with a
> > personalized color. Therefore, create a module parameter that takes a
> > unsigned long number as an XRGB16161616 color and set the background
> > color to it. That said, the composition will be performed on top of
> > this background color. By default, the background color is black.
> >
> > Signed-off-by: Maíra Canal <mcanal@xxxxxxxxxx>
> > ---
> >
> > This patch intends to add a background color property to vkms through
> > a module parameter. Another option would be to implement this property
> > by adding a new KMS property that would indicate the background color.
> > It would be nice to hear other opinions on what would be the best
> > approach.
>
> These patches (and I think even igts for them) have been floating
> around for years. The hang-up is the userspace. Turns out all
> compositors want for background is black, thus far no one has figured
> out a real use-case for anything else.
>
> Maybe some time ...

But, would it be okay to add this feature as a vkms' module parameter?

> > Moreover, I wrote some IGT tests to ensure that the functionality is
> > working correctly [1]. The tests take the CRC of a colored primary
> > plane, offset the primary plane out of the screen, and take the CRC
> > of the colored background. The two CRC must be equal.
> >
> > [1] https://gitlab.freedesktop.org/mairacanal/igt-gpu-tools/-/tree/vkms/background-color
>
> I wonder whether it would be more useful to have this as a Kunit
> validation test to very that the vkms composing code works correctly?
> Still with the modparam and vkms_config to handle it all cleanly.

Not sure if this would fit as a unit test, as the vkms composing
code basically outputs a CRC, which can be better verified by
the userspace. The output_buffer and stage_buffer are internal
variables, so it would be difficult to evaluate them with a KUnit
test.

With the IGT test, we can assure that the background composition
is being performed properly using the CRC in a negative test and
also some positive tests.

Best Regards,
- Maíra Canal

> -Daniel
>
> > Best Regards,
> > - Maíra Canal
> >
> > ---
> >   Documentation/gpu/vkms.rst           |  2 --
> >   drivers/gpu/drm/vkms/vkms_composer.c | 20 ++++++++++++++------
> >   drivers/gpu/drm/vkms/vkms_drv.c      |  6 ++++++
> >   drivers/gpu/drm/vkms/vkms_drv.h      |  4 ++++
> >   4 files changed, 24 insertions(+), 8 deletions(-)
> >
> > diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> > index 49db221c0f52..dc01689d8c76 100644
> > --- a/Documentation/gpu/vkms.rst
> > +++ b/Documentation/gpu/vkms.rst
> > @@ -121,8 +121,6 @@ There's lots of plane features we could add support for:
> >   - ARGB format on primary plane: blend the primary plane into background with
> >     translucent alpha.
> >
> > -- Add background color KMS property[Good to get started].
> > -
> >   - Full alpha blending on all planes.
> >
> >   - Rotation, scaling.
> > diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> > index 8e53fa80742b..07345faee98a 100644
> > --- a/drivers/gpu/drm/vkms/vkms_composer.c
> > +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> > @@ -79,7 +79,8 @@ static void fill_background(const struct pixel_argb_u16 *background_color,
> >    * from all planes, calculates the crc32 of the output from the former step,
> >    * and, if necessary, convert and store the output to the writeback buffer.
> >    */
> > -static void blend(struct vkms_writeback_job *wb,
> > +static void blend(struct vkms_device *vkms_dev,
> > +                 struct vkms_writeback_job *wb,
> >                    struct vkms_crtc_state *crtc_state,
> >                    u32 *crc32, struct line_buffer *stage_buffer,
> >                    struct line_buffer *output_buffer, size_t row_size)
> > @@ -87,7 +88,12 @@ static void blend(struct vkms_writeback_job *wb,
> >          struct vkms_plane_state **plane = crtc_state->active_planes;
> >          u32 n_active_planes = crtc_state->num_active_planes;
> >
> > -       const struct pixel_argb_u16 background_color = { .a = 0xffff };
> > +       const struct pixel_argb_u16 background_color = {
> > +               .a =  0xffff,
> > +               .r = (*vkms_dev->config->background_color >> 32) & 0xffff,
> > +               .g = (*vkms_dev->config->background_color >> 16) & 0xffff,
> > +               .b = *vkms_dev->config->background_color & 0xffff,
> > +       };
> >
> >          size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;
> >
> > @@ -139,7 +145,8 @@ static int check_iosys_map(struct vkms_crtc_state *crtc_state)
> >          return 0;
> >   }
> >
> > -static int compose_active_planes(struct vkms_writeback_job *active_wb,
> > +static int compose_active_planes(struct vkms_device *vkms_dev,
> > +                                struct vkms_writeback_job *active_wb,
> >                                   struct vkms_crtc_state *crtc_state,
> >                                   u32 *crc32)
> >   {
> > @@ -178,7 +185,7 @@ static int compose_active_planes(struct vkms_writeback_job *active_wb,
> >                  goto free_stage_buffer;
> >          }
> >
> > -       blend(active_wb, crtc_state, crc32, &stage_buffer,
> > +       blend(vkms_dev, active_wb, crtc_state, crc32, &stage_buffer,
> >                &output_buffer, line_width * pixel_size);
> >
> >          kvfree(output_buffer.pixels);
> > @@ -205,6 +212,7 @@ void vkms_composer_worker(struct work_struct *work)
> >          struct drm_crtc *crtc = crtc_state->base.crtc;
> >          struct vkms_writeback_job *active_wb = crtc_state->active_writeback;
> >          struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> > +       struct vkms_device *vkms_dev = vkms_output_to_vkms_device(out);
> >          bool crc_pending, wb_pending;
> >          u64 frame_start, frame_end;
> >          u32 crc32 = 0;
> > @@ -228,9 +236,9 @@ void vkms_composer_worker(struct work_struct *work)
> >                  return;
> >
> >          if (wb_pending)
> > -               ret = compose_active_planes(active_wb, crtc_state, &crc32);
> > +               ret = compose_active_planes(vkms_dev, active_wb, crtc_state, &crc32);
> >          else
> > -               ret = compose_active_planes(NULL, crtc_state, &crc32);
> > +               ret = compose_active_planes(vkms_dev, NULL, crtc_state, &crc32);
> >
> >          if (ret)
> >                  return;
> > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> > index 6d3a2d57d992..a4938dcb8c3e 100644
> > --- a/drivers/gpu/drm/vkms/vkms_drv.c
> > +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> > @@ -51,6 +51,10 @@ static bool enable_overlay;
> >   module_param_named(enable_overlay, enable_overlay, bool, 0444);
> >   MODULE_PARM_DESC(enable_overlay, "Enable/Disable overlay support");
> >
> > +static unsigned long background_color = 0x000000000000;
> > +module_param_named(background_color, background_color, ulong, 0644);
> > +MODULE_PARM_DESC(background_color, "Background color (0xRRRRGGGGBBBB)");
> > +
> >   DEFINE_DRM_GEM_FOPS(vkms_driver_fops);
> >
> >   static void vkms_release(struct drm_device *dev)
> > @@ -99,6 +103,7 @@ static int vkms_config_show(struct seq_file *m, void *data)
> >          seq_printf(m, "writeback=%d\n", vkmsdev->config->writeback);
> >          seq_printf(m, "cursor=%d\n", vkmsdev->config->cursor);
> >          seq_printf(m, "overlay=%d\n", vkmsdev->config->overlay);
> > +       seq_printf(m, "background_color=0x%lx\n", *vkmsdev->config->background_color);
> >
> >          return 0;
> >   }
> > @@ -226,6 +231,7 @@ static int __init vkms_init(void)
> >          config->cursor = enable_cursor;
> >          config->writeback = enable_writeback;
> >          config->overlay = enable_overlay;
> > +       config->background_color = &background_color;
> >
> >          ret = vkms_create(config);
> >          if (ret)
> > diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> > index 4a248567efb2..4bc2e6a6d219 100644
> > --- a/drivers/gpu/drm/vkms/vkms_drv.h
> > +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> > @@ -113,6 +113,7 @@ struct vkms_config {
> >          bool writeback;
> >          bool cursor;
> >          bool overlay;
> > +       unsigned long *background_color;
> >          /* only set when instantiated */
> >          struct vkms_device *dev;
> >   };
> > @@ -127,6 +128,9 @@ struct vkms_device {
> >   #define drm_crtc_to_vkms_output(target) \
> >          container_of(target, struct vkms_output, crtc)
> >
> > +#define vkms_output_to_vkms_device(target) \
> > +       container_of(target, struct vkms_device, output)
> > +
> >   #define drm_device_to_vkms_device(target) \
> >          container_of(target, struct vkms_device, drm)
> >
> > --
> > 2.39.2