Hi Am 28.01.22 um 12:04 schrieb Laurent Pinchart: > Hi Thomas, > > On Fri, Jan 28, 2022 at 11:46:49AM +0100, Thomas Zimmermann wrote: >> Am 28.01.22 um 11:34 schrieb Laurent Pinchart: >>> On Fri, Jan 28, 2022 at 10:33:21AM +0100, Thomas Zimmermann wrote: >>>> Am 28.01.22 um 10:13 schrieb Kieran Bingham: >>>>> 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. >>> >>> I doubt that's going to work as you expect, clocks and regulators will >>> get disabled at boot if not used by any driver. >> >> Simpledrm and simplefb attach to these firmware framebuffers. Both >> drivers look at the device tree nodes to acquire the relevant clocks and >> regulators. > > How about clocks and regulators for the ancillary devices, such as > encoders, or in the R-Car case, the external composer handled by the > vsp1 driver (in drivers/media/platform/vsp1) ? > > This approach may work fine on x86 desktop systems, but for ARM-based > devices, the situation is usually more complex. Well, in that case the problem has always been there. We don't make it worse. 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); > -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev