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

Paul Cercueil
2021-08-05T20:05:37Z

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 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