Re: [PATCH 2/2] gpu/drm: ingenic: Add workaround for disabled drivers

[Paul Cercueil]

Hi Greg,

Le jeu., août 5 2021 at 21:35:34 +0200, Greg Kroah-Hartman 
<gregkh@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> >  ---
> >   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 driver from
> >  +			 * 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.

> 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.

Cheers,
-Paul