Hi Am 28.01.22 um 10:13 schrieb Kieran Bingham: > Hi Javier, > > Quoting Javier Martinez Canillas (2021-12-17 00:37:46) >> According to disable Documentation/admin-guide/kernel-parameters.txt, this >> parameter can be used to disable kernel modesetting. >> >> DRM drivers will not perform display-mode changes or accelerated rendering >> and only the system framebuffer will be available if it was set-up. > > What is the 'system framebuffer' in this instance? Reading > https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt > it sounds like that means anything already set up by the bootloader. Exactly this. > >> But only a few DRM drivers currently check for nomodeset, make this driver >> to also support the command line parameter. >> >> Signed-off-by: Javier Martinez Canillas >> --- >> >> (no changes since v1) >> >> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c >> index 5a8131ef81d5..982e450233ed 100644 >> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c >> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c >> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = { >> >> static int __init rcar_du_init(void) >> { >> + if (drm_firmware_drivers_only()) >> + return -ENODEV; >> + > > This will completely disable all control of the display device when > nomodeset is enabled. > > Is there any requirement for us to support outputting to the display if > it was previously set up? presumably without setting or changing any > modes, but simply allowing the existing frame to be updated? There's no requirement for your driver. We just want a parameter where we can conveniently disable most of DRM's drivers and reduce it to a minimum. Helps distributions to provide a simple fallback mode. Most PCI-based drivers already support that. Now we're added it to the other drivers as well. > > I think the implication is that 'firmware drivers' would mean a display > could be updated through some firmware interface, which we won't have > ... so it seems reasonable to accept that this whole driver can be > disabled in that instance. It cannot be 'mode-setted'. We get a pre-configured framebuffer from the firmware or bootloader. Whatever we draw there shows up on the screen. Best regards Thomas > > Reading your mail that brought this thread up in my inbox, I think > you've already hit merge on this, so don't worry about adding a tag in > that instance, but I think this is ok. > > Reviewed-by: Kieran Bingham > >> rcar_du_of_init(rcar_du_of_table); >> >> return platform_driver_register(&rcar_du_platform_driver); >> -- >> 2.33.1 >> -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev