Hi Am 14.12.21 um 09:30 schrieb Javier Martinez Canillas:
Hello Maxime On Mon, Dec 13, 2021 at 5:26 PM Maxime Ripard <maxime@xxxxxxxxxx> wrote:If we have nomodeset on the kernel command line we should have the firmware framebuffer driver kept as is and not try to load the full-blown KMS driver.Patch looks good to me. I just have a question, but I'm OK with either way. Reviewed-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>In this case, let's just register the v3d driver.I wonder if the v3d driver should be registered if nomodeset is present. Most (if not all?) drivers that currently check for this parameter disable both KMS and DRM. So even when it seems to imply that's about kernel mode settings, it is also used to disable DRM. This semantic was never documented and I attempted to do that in commit b22a15a5aca3 ("Documentation/admin-guide: Document nomodeset kernel parameter"). After feedback from folks in the list, the text ended as follows: ``` Disable kernel modesetting. DRM drivers will not perform display-mode changes or accelerated rendering. Only the system framebuffer will be available for use if this was set-up by the firmware or boot loader. Useful as fallback, or for testing and debugging. ``` So maybe vc4_drm_register() should just return -EINVAL if (drm_firmware_drivers_only()) like the other drivers do?
I second this comment. The intention of this test is to disable HW-native drivers if something goes wrong with the display.
The function's name drm_firmware_drivers_only() reflects that. The parameter is called nomodeset for historical reasons and it's probably a terrible name.
So I think the code should call drm_firmware_drivers_only() at the top and return an error is it's true. That's what we will do for other drivers as well. Maybe rather return -ENODEV; EINVAL mean 'invalid argument'.
Best regards Thomas
Best regards, Javier
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
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