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From: Paul Cercueil <paul@crapouillou.net>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rob Herring <robh@kernel.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Sam Ravnborg <sam@ravnborg.org>,
	list@opendingux.net, linux-kernel@vger.kernel.org,
	linux-mips@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 2/2] gpu/drm: ingenic: Add workaround for disabled drivers
Date: Thu, 05 Aug 2021 22:05:27 +0200	[thread overview]
Message-ID: <3HUDXQ.7RBGD4FUHR2F@crapouillou.net> (raw)
In-Reply-To: <YQw9hjZll4QmYVLX@kroah.com>

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



  reply	other threads:[~2021-08-05 20:05 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-05 19:21 [PATCH 0/2] gpu/drm: ingenic: Handle " Paul Cercueil
2021-08-05 19:21 ` [PATCH 1/2] drivers core: Export driver_deferred_probe_check_state() Paul Cercueil
2021-08-05 19:34   ` Greg Kroah-Hartman
2021-08-05 19:21 ` [PATCH 2/2] gpu/drm: ingenic: Add workaround for disabled drivers Paul Cercueil
2021-08-05 19:35   ` Greg Kroah-Hartman
2021-08-05 20:05     ` Paul Cercueil [this message]
2021-08-06 10:17       ` Greg Kroah-Hartman
2021-08-06 11:01         ` Paul Cercueil
2021-08-10  9:35           ` Daniel Vetter
2021-08-10 10:33             ` Paul Cercueil
2021-08-10 10:59               ` Daniel Vetter
2021-08-10 11:58                 ` Paul Cercueil
2021-08-10  9:47           ` Greg Kroah-Hartman
2021-08-10 10:40             ` Paul Cercueil
2021-08-10 10:52               ` Daniel Vetter

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