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

["José Expósito" <jose.exposito89@gmail.com>]

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
> >