Re: [PATCH 07/13] drm/vkms: Allow to configure multiple planes

José Expósito
2025-02-11T10:43:27Z

On Thu, Jan 30, 2025 at 02:48:19PM +0100, Louis Chauvet wrote:
> On 29/01/25 - 12:00, José Expósito wrote:
> > Add a list of planes to vkms_config and create as many planes as
> > configured during output initialization.
> >
> > For backwards compatibility, add one primary plane and, if configured,
> > one cursor plane and NUM_OVERLAY_PLANES planes to the default
> > configuration.
> >
> > Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> > Signed-off-by: José Expósito <jose.exposito89@gmail.com>
>
> Co-developped-by: Louis Chauvet <louis.chauvet@bootlin.com>
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> Signed-off-by: José Expósito <jose.exposito89@gmail.com>
>
> [...]
>
> > diff --git a/drivers/gpu/drm/vkms/tests/vkms_config_test.c b/drivers/gpu/drm/vkms/tests/vkms_config_test.c
>
> [...]
>
> > +static void vkms_config_test_get_planes(struct kunit *test)
> > +{
> > + struct vkms_config *config;
> > + struct vkms_config_plane *plane_cfg1, *plane_cfg2;
> > + struct vkms_config_plane **array;
> > + size_t length;
> > +
> > + config = vkms_config_create("test");
> > + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, config);
> > +
> > + array = vkms_config_get_planes(config, &length);
> > + KUNIT_ASSERT_EQ(test, length, 0);
> > + KUNIT_ASSERT_NULL(test, array);
> > +
> > + plane_cfg1 = vkms_config_add_plane(config);
> > + array = vkms_config_get_planes(config, &length);
> > + KUNIT_ASSERT_EQ(test, length, 1);
> > + KUNIT_ASSERT_PTR_EQ(test, array[0], plane_cfg1);
> > + kfree(array);
> > +
> > + plane_cfg2 = vkms_config_add_plane(config);
> > + array = vkms_config_get_planes(config, &length);
> > + KUNIT_ASSERT_EQ(test, length, 2);
> > + KUNIT_ASSERT_PTR_EQ(test, array[0], plane_cfg1);
> > + KUNIT_ASSERT_PTR_EQ(test, array[1], plane_cfg2);
> > + kfree(array);
> > +
> > + vkms_config_destroy_plane(plane_cfg1);
> > + array = vkms_config_get_planes(config, &length);
> > + KUNIT_ASSERT_EQ(test, length, 1);
> > + KUNIT_ASSERT_PTR_EQ(test, array[0], plane_cfg2);
> > + kfree(array);
> > +
> > + vkms_config_destroy(config);
> > +}
>
> In this test I have the feeling that vkms_config_get_planes always returns
> a predictable order. It is maybe trivial here, but I would prefer to shows
> that the order is not stable, for example:
>
> bool plane_cfg1_found = false;
> bool plane_cfg2_found = false;
>
> vkms_config_for_each_plane(config, plane_cfg) {
> if (plane_cfg == plane_cfg1)
> plane_cfg1_found = true;
> else if (plane_cfg == plane_cfg2)
> plane_cfg2_found = true;
> else
> KUNIT_FAILS("Unexpected plane");
> }
>
> KUNIT_ASSERT(test, plane_cfg1_found);
> KUNIT_ASSERT(test, plane_cfg2_found);
>
> [...]
>
> > +static void vkms_config_test_valid_plane_number(struct kunit *test)
> > +{
> > + struct vkms_config *config;
> > + struct vkms_config_plane *plane_cfg;
> > + int n;
> > +
> > + config = vkms_config_default_create(false, false, false);
> > + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, config);
> > +
> > + /* Invalid: No planes */
> > + plane_cfg = list_first_entry(&config->planes, typeof(*plane_cfg), link);
> > + vkms_config_destroy_plane(plane_cfg);
> > + KUNIT_EXPECT_FALSE(test, vkms_config_is_valid(config));
> > +
> > + /* Invalid: Too many planes */
> > + for (n = 0; n <= 32; n++)
> > + vkms_config_add_plane(config);
> > +
> > + KUNIT_EXPECT_FALSE(test, vkms_config_is_valid(config));
> > +
> > + vkms_config_destroy(config);
> > +}
>
> For this function, the naming is a bit strange, it says
> "valid_plane_number", but you test only invalid plane number.

The reason for this naming is that it tests the valid_plane_number()
function called by vkms_config_is_valid(). The applies for the other
valid_* tests.

However, I don't mind changing its name to so it reflects the test
rather than the tested function.

Changed in v2.

>
> Can you rename it to vkms_config_test_invalid_plane_number?
>
> [...]
>
> > diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
>
> [...]
>
> > +struct vkms_config_plane **vkms_config_get_planes(const struct vkms_config *config,
> > + size_t *out_length)
> > +{
> > + struct vkms_config_plane **array;
> > + struct vkms_config_plane *plane_cfg;
> > + size_t length;
> > + int n = 0;
> > +
> > + length = list_count_nodes((struct list_head *)&config->planes);
> > + if (length == 0) {
> > + *out_length = length;
> > + return NULL;
> > + }
> > +
> > + array = kmalloc_array(length, sizeof(*array), GFP_KERNEL);
> > + if (!array)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + list_for_each_entry(plane_cfg, &config->planes, link) {
> > + array[n] = plane_cfg;
> > + n++;
> > + }
> > +
> > + *out_length = length;
> > + return array;
> > +}
>
> To join the comment on the test, I am not a big fan of creating a new list
> to return to the caller, for three reasons:
> - the caller needs to manage an other pointer;
> - the caller needs to understand that the content of the array is only
> valid if: the config is not freed, nobody else removed anything from the
> planes;
> - the caller may think this list always have the same order if he looks at
> the tests.
>
> I would prefer a simple macro to do an iteration over the config->planes
> list: (I did not test this macro, but you have this idea)
>
> #define vkms_config_iter_plane(config, plane_cfg) \
> list_for_each_entry((plane_cfg), &(config).planes, link)
>
> This way:
> - no new pointer to manage;
> - if one day we have concurency issue, we just have to protect config, not
> config+all the planes;
> - there is no expected order.
>
> [...]
>
> > bool vkms_config_is_valid(struct vkms_config *config)
> > {
> > + if (!valid_plane_number(config))
> > + return false;
> > +
> > + if (!valid_plane_type(config))
> > + return false;
> > +
> > return true;
> > }
>
> I really like the idea to split the validation function, way simpler!
>
> [...]
>
> > +void vkms_config_destroy_plane(struct vkms_config_plane *plane_cfg)
> > +{
> > + list_del(&plane_cfg->link);
> > + kfree(plane_cfg);
> > +}
>
> I would prefer a "standard" function pair, i.e.: add/remove or
> create/destroy, not add/destroy.
>
> For me it should be create/destroy, you create the plane by using a
> config, so it is clear it will be attached to it.
>
> If you choose add/remove, you should explains in the documentation that
> remove is also doing kfree.
>
> [...]
>
> > diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
>
> [...]
>
> > @@ -11,61 +11,63 @@ int vkms_output_init(struct vkms_device *vkmsdev)
> > struct vkms_connector *connector;
> > struct drm_encoder *encoder;
> > struct vkms_output *output;
> > - struct vkms_plane *primary, *overlay, *cursor = NULL;
> > - int ret;
> > + struct vkms_plane *primary = NULL, *cursor = NULL;
> > + struct vkms_config_plane **plane_cfgs = NULL;
> > + size_t n_planes;
> > + int ret = 0;
> > int writeback;
> > unsigned int n;
>
> I think it could be interesting to have a vkms_config_is_valid call here.
> It will avoid raising DRM errors or create unexpected devices.
>
> It will also garantee in a later patch that
> vkms_config_crtc_get_primary_plane is a valid pointer.
>
> > - /*
> > - * Initialize used plane. One primary plane is required to perform the composition.
> > - *
> > - * The overlay and cursor planes are not mandatory, but can be used to perform complex
> > - * composition.
> > - */
> > - primary = vkms_plane_init(vkmsdev, DRM_PLANE_TYPE_PRIMARY);
> > - if (IS_ERR(primary))
> > - return PTR_ERR(primary);
> > + plane_cfgs = vkms_config_get_planes(vkmsdev->config, &n_planes);
> > + if (IS_ERR(plane_cfgs))
> > + return PTR_ERR(plane_cfgs);
>
> If you agree on the iterator implementation, this code could be simplified
> a lot.
>
> > - if (vkmsdev->config->cursor) {
> > - cursor = vkms_plane_init(vkmsdev, DRM_PLANE_TYPE_CURSOR);
> > - if (IS_ERR(cursor))
> > - return PTR_ERR(cursor);
> > + for (n = 0; n < n_planes; n++) {
> > + struct vkms_config_plane *plane_cfg;
> > + enum drm_plane_type type;
> > +
> > + plane_cfg = plane_cfgs[n];
> > + type = vkms_config_plane_get_type(plane_cfg);
> > +
> > + plane_cfg->plane = vkms_plane_init(vkmsdev, type);
>
> Can we pass plane_cfg in vkms_plane_init? This way we don't have to
> touch vkms_output_init when adding new vkms_config_plane members.

While it'll be required once we allow to configure more parameters, I don't
think we need it right now. To keep things as simple as possible, I'd prefer to
delay it until required.

Thanks,
Jose

> > + if (IS_ERR(plane_cfg->plane)) {
> > + DRM_DEV_ERROR(dev->dev, "Failed to init vkms plane\n");
> > + ret = PTR_ERR(plane_cfg->plane);
> > + goto err_free;
> > + }
> > +
> > + if (type == DRM_PLANE_TYPE_PRIMARY)
> > + primary = plane_cfg->plane;
> > + else if (type == DRM_PLANE_TYPE_CURSOR)
> > + cursor = plane_cfg->plane;
> > }
>
> …