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

[Maíra Canal <mcanal@xxxxxxxxxx>]

On 4/6/23 15:23, Daniel Vetter wrote:
> On Thu, Apr 06, 2023 at 03:06:56PM -0300, Maíra Canal wrote:
> > 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?
>
> Yeah I think that's ok.
>
> > > > 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.
>
> I was just thinking of how you could keep the test, because igt is for
> uapi in general. So doesn't fit all that well, validating internals is
> more what kunit is supposed to do.

I'm not sure if testing the composition is an internal behavior, because
the output of the composition is a CRC that is exposed to the userspace.

Moreover, we need some sort of variable output to create a KUnit test,
which is not the case for vkms. The output_buffer and stage_buffer
are internal variables and they are overwritten on each iteration of
the blend loop.

As this property would be exclusive to vkms, I believe it would be okay
to add a vkms-specific IGT test to verify the correct behavior of the
background.

Best Regards,
- Maíra Canal

> -Daniel
>
> > 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