Re: [PATCH 07/13] drm/vkms: Allow to configure multiple planes

Louis Chauvet
2025-02-12T14:10:27Z

Le 11/02/2025 à 11:43, José Expósito a écrit :
> On Thu, Jan 30, 2025 at 02:48:19PM +0100, Louis Chauvet wrote:
>> On 29/01/25 - 12:00, José Expósito wrote:
>>> Add a list of planes to vkms_config and create as many planes as
>>> configured during output initialization.
>>>
>>> For backwards compatibility, add one primary plane and, if configured,
>>> one cursor plane and NUM_OVERLAY_PLANES planes to the default
>>> configuration.
>>>
>>> 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_get_planes(struct kunit *test)
>>> +{
>>> + struct vkms_config *config;
>>> + struct vkms_config_plane *plane_cfg1, *plane_cfg2;
>>> + struct vkms_config_plane **array;
>>> + size_t length;
>>> +
>>> + config = vkms_config_create("test");
>>> + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, config);
>>> +
>>> + array = vkms_config_get_planes(config, &length);
>>> + KUNIT_ASSERT_EQ(test, length, 0);
>>> + KUNIT_ASSERT_NULL(test, array);
>>> +
>>> + plane_cfg1 = vkms_config_add_plane(config);
>>> + array = vkms_config_get_planes(config, &length);
>>> + KUNIT_ASSERT_EQ(test, length, 1);
>>> + KUNIT_ASSERT_PTR_EQ(test, array[0], plane_cfg1);
>>> + kfree(array);
>>> +
>>> + plane_cfg2 = vkms_config_add_plane(config);
>>> + array = vkms_config_get_planes(config, &length);
>>> + KUNIT_ASSERT_EQ(test, length, 2);
>>> + KUNIT_ASSERT_PTR_EQ(test, array[0], plane_cfg1);
>>> + KUNIT_ASSERT_PTR_EQ(test, array[1], plane_cfg2);
>>> + kfree(array);
>>> +
>>> + vkms_config_destroy_plane(plane_cfg1);
>>> + array = vkms_config_get_planes(config, &length);
>>> + KUNIT_ASSERT_EQ(test, length, 1);
>>> + KUNIT_ASSERT_PTR_EQ(test, array[0], plane_cfg2);
>>> + kfree(array);
>>> +
>>> + vkms_config_destroy(config);
>>> +}
>>
>> In this test I have the feeling that vkms_config_get_planes always returns
>> a predictable order. It is maybe trivial here, but I would prefer to shows
>> that the order is not stable, for example:
>>
>> bool plane_cfg1_found = false;
>> bool plane_cfg2_found = false;
>>
>> vkms_config_for_each_plane(config, plane_cfg) {
>> if (plane_cfg == plane_cfg1)
>> plane_cfg1_found = true;
>> else if (plane_cfg == plane_cfg2)
>> plane_cfg2_found = true;
>> else
>> KUNIT_FAILS("Unexpected plane");
>> }
>>
>> KUNIT_ASSERT(test, plane_cfg1_found);
>> KUNIT_ASSERT(test, plane_cfg2_found);
>>
>> [...]
>>
>>> +static void vkms_config_test_valid_plane_number(struct kunit *test)
>>> +{
>>> + struct vkms_config *config;
>>> + struct vkms_config_plane *plane_cfg;
>>> + int n;
>>> +
>>> + config = vkms_config_default_create(false, false, false);
>>> + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, config);
>>> +
>>> + /* Invalid: No planes */
>>> + plane_cfg = list_first_entry(&config->planes, typeof(*plane_cfg), link);
>>> + vkms_config_destroy_plane(plane_cfg);
>>> + KUNIT_EXPECT_FALSE(test, vkms_config_is_valid(config));
>>> +
>>> + /* Invalid: Too many planes */
>>> + for (n = 0; n <= 32; n++)
>>> + vkms_config_add_plane(config);
>>> +
>>> + KUNIT_EXPECT_FALSE(test, vkms_config_is_valid(config));
>>> +
>>> + vkms_config_destroy(config);
>>> +}
>>
>> For this function, the naming is a bit strange, it says
>> "valid_plane_number", but you test only invalid plane number.
>
> The reason for this naming is that it tests the valid_plane_number()
> function called by vkms_config_is_valid(). The applies for the other
> valid_* tests.

Hoo, I see, okk!

> However, I don't mind changing its name to so it reflects the test
> rather than the tested function.

I prefer an "implementation independent" name, as the content of
vkms_config_is_valid may change over time.

> Changed in v2.

Perfect!

>>
>> Can you rename it to vkms_config_test_invalid_plane_number?
>>
>> [...]
>>
>>> diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
>>
>> [...]
>>
>>> +struct vkms_config_plane **vkms_config_get_planes(const struct vkms_config *config,
>>> + size_t *out_length)
>>> +{
>>> + struct vkms_config_plane **array;
>>> + struct vkms_config_plane *plane_cfg;
>>> + size_t length;
>>> + int n = 0;
>>> +
>>> + length = list_count_nodes((struct list_head *)&config->planes);
>>> + 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(plane_cfg, &config->planes, link) {
>>> + array[n] = plane_cfg;
>>> + n++;
>>> + }
>>> +
>>> + *out_length = length;
>>> + return array;
>>> +}
>>
>> To join the comment on the test, I am not a big fan of creating a new list
>> to return to the caller, for three reasons:
>> - the caller needs to manage an other pointer;
>> - the caller needs to understand that the content of the array is only
>> valid if: the config is not freed, nobody else removed anything from the
>> planes;
>> - the caller may think this list always have the same order if he looks at
>> the tests.
>>
>> I would prefer a simple macro to do an iteration over the config->planes
>> list: (I did not test this macro, but you have this idea)
>>
>> #define vkms_config_iter_plane(config, plane_cfg) \
>> list_for_each_entry((plane_cfg), &(config).planes, link)
>>
>> This way:
>> - no new pointer to manage;
>> - if one day we have concurency issue, we just have to protect config, not
>> config+all the planes;
>> - there is no expected order.
>>
>> [...]
>>
>>> bool vkms_config_is_valid(struct vkms_config *config)
>>> {
>>> + if (!valid_plane_number(config))
>>> + return false;
>>> +
>>> + if (!valid_plane_type(config))
>>> + return false;
>>> +
>>> return true;
>>> }
>>
>> I really like the idea to split the validation function, way simpler!
>>
>> [...]
>>
>>> +void vkms_config_destroy_plane(struct vkms_config_plane *plane_cfg)
>>> +{
>>> + list_del(&plane_cfg->link);
>>> + kfree(plane_cfg);
>>> +}
>>
>> I would prefer a "standard" function pair, i.e.: add/remove or
>> create/destroy, not add/destroy.
>>
>> For me it should be create/destroy, you create the plane by using a
>> config, so it is clear it will be attached to it.
>>
>> If you choose add/remove, you should explains in the documentation that
>> remove is also doing kfree.
>>
>> [...]
>>
>>> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
>>
>> [...]
>>
>>> @@ -11,61 +11,63 @@ int vkms_output_init(struct vkms_device *vkmsdev)
>>> struct vkms_connector *connector;
>>> struct drm_encoder *encoder;
>>> struct vkms_output *output;
>>> - struct vkms_plane *primary, *overlay, *cursor = NULL;
>>> - int ret;
>>> + struct vkms_plane *primary = NULL, *cursor = NULL;
>>> + struct vkms_config_plane **plane_cfgs = NULL;
>>> + size_t n_planes;
>>> + int ret = 0;
>>> int writeback;
>>> unsigned int n;
>>
>> I think it could be interesting to have a vkms_config_is_valid call here.
>> It will avoid raising DRM errors or create unexpected devices.
>>
>> It will also garantee in a later patch that
>> vkms_config_crtc_get_primary_plane is a valid pointer.
>>
>>> - /*
>>> - * Initialize used plane. One primary plane is required to perform the composition.
>>> - *
>>> - * The overlay and cursor planes are not mandatory, but can be used to perform complex
>>> - * composition.
>>> - */
>>> - primary = vkms_plane_init(vkmsdev, DRM_PLANE_TYPE_PRIMARY);
>>> - if (IS_ERR(primary))
>>> - return PTR_ERR(primary);
>>> + plane_cfgs = vkms_config_get_planes(vkmsdev->config, &n_planes);
>>> + if (IS_ERR(plane_cfgs))
>>> + return PTR_ERR(plane_cfgs);
>>
>> If you agree on the iterator implementation, this code could be simplified
>> a lot.
>>
>>> - if (vkmsdev->config->cursor) {
>>> - cursor = vkms_plane_init(vkmsdev, DRM_PLANE_TYPE_CURSOR);
>>> - if (IS_ERR(cursor))
>>> - return PTR_ERR(cursor);
>>> + for (n = 0; n < n_planes; n++) {
>>> + struct vkms_config_plane *plane_cfg;
>>> + enum drm_plane_type type;
>>> +
>>> + plane_cfg = plane_cfgs[n];
>>> + type = vkms_config_plane_get_type(plane_cfg);
>>> +
>>> + plane_cfg->plane = vkms_plane_init(vkmsdev, type);
>>
>> Can we pass plane_cfg in vkms_plane_init? This way we don't have to
>> touch vkms_output_init when adding new vkms_config_plane members.
>
> While it'll be required once we allow to configure more parameters, I don't
> think we need it right now. To keep things as simple as possible, I'd prefer to
> delay it until required.

I understand your point, especially since your patch don't add new
parameters to vkms_plane_init.

Thanks!

> Thanks,
> Jose
>
>>> + if (IS_ERR(plane_cfg->plane)) {
>>> + DRM_DEV_ERROR(dev->dev, "Failed to init vkms plane\n");
>>> + ret = PTR_ERR(plane_cfg->plane);
>>> + goto err_free;
>>> + }
>>> +
>>> + if (type == DRM_PLANE_TYPE_PRIMARY)
>>> + primary = plane_cfg->plane;
>>> + else if (type == DRM_PLANE_TYPE_CURSOR)
>>> + cursor = plane_cfg->plane;
>>> }
>>
>> [...]

--
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering