Hi Daniel,
Le mar., août 10 2021 at 11:35:43 +0200, Daniel Vetter daniel@ffwll.ch a écrit :
On Fri, Aug 06, 2021 at 01:01:33PM +0200, Paul Cercueil wrote:
Hi Greg,
Le ven., août 6 2021 at 12:17:55 +0200, Greg Kroah-Hartman gregkh@linuxfoundation.org a écrit :
On Thu, Aug 05, 2021 at 10:05:27PM +0200, Paul Cercueil wrote:
Hi Greg,
Le jeu., août 5 2021 at 21:35:34 +0200, Greg Kroah-Hartman gregkh@linuxfoundation.org a écrit :
On Thu, Aug 05, 2021 at 09:21:09PM +0200, Paul Cercueil
wrote:
When the drivers of remote devices (e.g. HDMI chip) are
disabled in
the config, we want the ingenic-drm driver to be able to probe nonetheless with the other devices (e.g. internal LCD panel) that are
enabled.
Signed-off-by: Paul Cercueil paul@crapouillou.net
drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 12
++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c index d261f7a03b18..5e1fdbb0ba6b 100644 --- a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c +++ b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c @@ -1058,6 +1058,18 @@ static int ingenic_drm_bind(struct
device
*dev, bool has_components) for (i = 0; ; i++) { ret = drm_of_find_panel_or_bridge(dev->of_node, 0, i,
&panel,
&bridge); if (ret) {
/** Workaround for the case where the drivers for the* remote devices are not enabled. When that happens,* drm_of_find_panel_or_bridge() returns -EPROBE_DEFER* endlessly, which prevents the ingenic-drm driverfrom
* working at all.*/if (ret == -EPROBE_DEFER) {ret = driver_deferred_probe_check_state(dev);if (ret == -ENODEV || ret == -ETIMEDOUT)continue;}So you are mucking around with devices on other busses
within this
driver? What could go wrong? :(
I'm doing the same thing as everybody else. This is the DRM
driver,
and there is a driver for the external HDMI chip which gives us a
DRM
bridge that we can obtain from the device tree.
But then why do you need to call this function that is there for
a bus,
not for a driver.
The documentation disagrees with you :)
And, if that has any weight, this solution was proposed by Rob.
Please use the existing driver core functionality for this
type of
thing, it is not unique, no need for this function to be
called.
I'm not sure you understand what I'm doing here. This driver
calls
drm_of_find_panel_or_bridge(), without guarantee that the
driver
for the remote device (connected via DT graph) has been enabled in the kernel config. In that case it will always return -EPROBE_DEFER and
the
ingenic-drm driver will never probe.
This patch makes sure that the driver can probe if the HDMI
driver
has been disabled in the kernel config, nothing more.
That should not be an issue as you do not care if the config is
enabled,
you just want to do something in the future if the driver shows
up,
right?
Well, the DRM subsystem doesn't really seem to handle hotplug of hardware. Right now all the drivers for the connected hardware need to probe before the main DRM driver. So I need to know that a remote device (connected via DT graph) will never probe.
Give me a of_graph_remote_device_driver_will_never_probe() and I'll use that.
Much like the device link code, have you looked at that?
I don't see how that would help in any way. The device link code would allow me to set a dependency between the remote hardware (HDMI chip, provider) and the LCD controller (consumer), but I already have that dependency though the DT graph. What I need is a way for the consumer to continue probing if the provider is not going to probe.
Is this actually a legit use-case?
Like you have hw with a bunch of sub-devices linked, and you decided to disable some of them, which makes the driver not load.
Yes. I'm facing that issue with a board that has a LCD panel and a HDMI controller (IT66121). I have a "flasher" program for all the Ingenic boards, that's basically just a Linux kernel + initramfs booted over USB (device). I can't realistically enable every single driver for all the hardware that's on these boards while still having a tiny footprint. And I shouldn't have to care about it either.
Why should we care? Is that hdmi driver really that big that we have to support this use-case?
DRM maintainers work with what embedded devs would call "infinite resources". It annoys me that CONFIG_DRM pulls the I2C code even though I may just have a LCD panel, and it annoys me that I have to enable support for hardware that I'm not even planning to use, just so that the DRM driver works for the hardware I do want to use.
I know it's possible to do this, that doesn't mean it's a good idea. There's inifinitely more randconfigs that don't boot on my machine here for various reasons than the ones that do boot. We don't have "fixes" for all of these to make things still work, despite user misconfiguring their kernel.
I understand, you can't really expect random configs to work every time. But it should still be possible to disable drivers for *optional* hardware in the config and end up with a working system.
Cheers, -Paul