Re: [PATCH 08/13] drm/vkms: Allow to configure multiple CRTCs

José Expósito
2025-02-11T10:44:40Z

On Thu, Jan 30, 2025 at 02:48:20PM +0100, Louis Chauvet wrote:
> On 29/01/25 - 12:00, José Expósito wrote:
> > Add a list of CRTCs to vkms_config and helper functions to add and
> > remove as many CRTCs as wanted.
> >
> > For backwards compatibility, add one CRTC to the default configuration.
> >
> > A future patch will allow to attach planes and CRTCs, but for the
> > moment there are no changes in the way the output is configured.
> >
> > 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_valid_crtc_number(struct kunit *test)
> > +{
> > + struct vkms_config *config;
> > + struct vkms_config_crtc *crtc_cfg;
> > + int n;
> > +
> > + config = vkms_config_default_create(false, false, false);
> > + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, config);
> > +
> > + /* Invalid: No CRTCs */
> > + crtc_cfg = list_first_entry(&config->crtcs, typeof(*crtc_cfg), link);
> > + vkms_config_destroy_crtc(config, crtc_cfg);
> > + KUNIT_EXPECT_FALSE(test, vkms_config_is_valid(config));
> > +
> > + /* Invalid: Too many CRTCs */
> > + for (n = 0; n <= 32; n++)
> > + vkms_config_add_crtc(config);
> > +
> > + KUNIT_EXPECT_FALSE(test, vkms_config_is_valid(config));
> > +
> > + vkms_config_destroy(config);
> > +}
>
> Same as before, can you rename the fonction to
> vkms_config_test_invalid_crtc_number
>
> [...]
>
> > diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
>
> [...]
>
> > +struct vkms_config_crtc **vkms_config_get_crtcs(const struct vkms_config *config,
> > + size_t *out_length)
> > +{
> > + struct vkms_config_crtc **array;
> > + struct vkms_config_crtc *crtc_cfg;
> > + size_t length;
> > + int n = 0;
> > +
> > + length = list_count_nodes((struct list_head *)&config->crtcs);
> > + 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(crtc_cfg, &config->crtcs, link) {
> > + array[n] = crtc_cfg;
> > + n++;
> > + }
> > +
> > + *out_length = length;
> > + return array;
> > +}
>
> Same as before, can't we use an iterator?
>
> [...]
>
> > +static bool valid_crtc_number(struct vkms_config *config)
> > +{
> > + size_t n_crtcs;
> > +
> > + n_crtcs = list_count_nodes(&config->crtcs);
> > + if (n_crtcs <= 0 || n_crtcs >= 32) {
> > + pr_err("The number of CRTCs must be between 1 and 31\n");
>
> I agree we need some logs, but I think pr_err is too agressive (i.e may
> be considered as an error by some test tools).
>
> I think we should at least:
> - lower to warn/notice/info
> - use drm variants of the macro
>
> > + return false;
> > + }
> > +
> > + return true;
> > +}
> > +
>
> [...]
>
> > +struct vkms_config_crtc *vkms_config_add_crtc(struct vkms_config *config)
> > +{
> > + struct vkms_config_crtc *crtc_cfg;
> > +
> > + crtc_cfg = kzalloc(sizeof(*crtc_cfg), GFP_KERNEL);
> > + if (!crtc_cfg)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + vkms_config_crtc_set_writeback(crtc_cfg, false);
> > +
> > + list_add_tail(&crtc_cfg->link, &config->crtcs);
> > +
> > + return crtc_cfg;
> > +}
> > +
> > +void vkms_config_destroy_crtc(struct vkms_config *config,
> > + struct vkms_config_crtc *crtc_cfg)
> > +{
> > + list_del(&crtc_cfg->link);
> > + kfree(crtc_cfg);
> > +}
>
> Same as before, the pair add/destroy seems strange.
>
> > +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> > @@ -181,7 +181,8 @@ static int vkms_create(struct vkms_config *config)
> > goto out_devres;
> > }
> >
> > - ret = drm_vblank_init(&vkms_device->drm, 1);
> > + ret = drm_vblank_init(&vkms_device->drm,
> > + vkms_config_get_num_crtcs(config));
>
> At this point we only create one crtc, can you move this change in the
> commit where you create multiple crtc?

Since the code to add more than one CRTCs is unused but technically present, I
think that this is the right patch to use this function.

Anyway, at the moment it'll always return 1, so it is a no-op.

I didn't change it in v2, let me know if it works for you.

Thanks,
Jose

> > if (ret) {
> > DRM_ERROR("Failed to vblank\n");
> > goto out_devres;
> > --
> > 2.48.1
> >