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

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Message-ID: <Z5uDJFHnn1HzWOz4@louis-chauvet-laptop>
Date: Thu, 30 Jan 2025 14:48:20 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: José Expósito <jose.exposito89@...il.com>
Cc: hamohammed.sa@...il.com, simona@...ll.ch, melissa.srw@...il.com,
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
	tzimmermann@...e.de, airlied@...il.com,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/13] drm/vkms: Allow to configure multiple CRTCs

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@...tlin.com>
> Signed-off-by: José Expósito <jose.exposito89@...il.com>

Co-developped-by: Louis Chauvet <louis.chauvet@...tlin.com>
Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
Signed-off-by: José Expósito <jose.exposito89@...il.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
>