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

Louis Chauvet
2025-02-12T14:12:17Z

Le 11/02/2025 à 11:44, José Expósito a écrit :
> 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.

I don't totally agree: you can create multiple vkms_config_crtc, but the
code only creates one drm_crtc.

For me it is more logical to keep 1 here, as the rest of the code only
creates one CRTC. With the next patch, the code will create more than
one CRTC, so it makes sense to use vkms_config_get_num_crtcs.

It is not a strong blocking point, but if a v3 is needed, could you
change it?

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

The current user is only default_config, so yes I agree, it is always 1.

> 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
>>>

--
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering