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

Louis Chauvet
2025-01-30T13:48:25Z

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?

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