Hi Thomas,
On Fri, Jan 28, 2022 at 12:26:03PM +0100, Thomas Zimmermann wrote:
Am 28.01.22 um 12:04 schrieb Laurent Pinchart:
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 <javierm@xxxxxxxxxx>
---
(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.
What's the point of adding nomodeset support in those drivers then, if
it's known not to work ?
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 <kieran.bingham+renesas@xxxxxxxxxxxxxxxx>
rcar_du_of_init(rcar_du_of_table);
return platform_driver_register(&rcar_du_platform_driver);
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