linux-kernel - Re: [PATCH] drm: change connector disconnected debug message to an error

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Date:   Fri, 03 Feb 2017 09:59:35 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Shuah Khan <shuahkh@....samsung.com>, daniel.vetter@...el.com,
        seanpaul@...omium.org, airlied@...ux.ie
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH] drm: change connector disconnected debug message to an error

On Thu, 02 Feb 2017, Shuah Khan <shuahkh@....samsung.com> wrote:
> On 02/02/2017 01:32 AM, Jani Nikula wrote:
>> On Thu, 02 Feb 2017, Shuah Khan <shuahkh@....samsung.com> wrote:
>>> Change drm_helper_probe_single_connector_modes() to print an error to
>>> report connector disconnected status instead of a debug message.
>>>
>>> When this condition occurs, application doesn't know the real error and
>>> reports it as driver lacking support for mode setting. Change it to an
>>> error to make it easier to debug.
>> 
>> Please explain what makes this condition an error. Connectors get
>> connected and disconnected, business as usual, why should this be an
>> error?
>> 
>> BR,
>> Jani.
>
> Disconnecting connector itself isn't an error. When user-space tries
> to access it, it would be useful to report the status that the connector
> is disconnected.
>
> I use embedded system(s) that don't like it when HDMI is hot added or
> removed. Also, because of return power, it is safer to disconnect HDMI
> and then apply power to the board. It chased a few libdrm and user-space
> dead ends before I enabled drm debug and was able to fix the real issue,
> which is a disconnected cable.
>
> User-space prints rather confusing messages as it doesn't really know
> the disconnected status as it isn't returned to it.
>
> I figured it might be a good idea to at least print a message and this can
> be a notice or info instead of an error. I do think its is worth while in
> some cases.

Well, I still think having a debug message for debugging is the way to
go, and that's what we have. Perhaps it is the userspace messages that
need improvement instead?

BR,
Jani.


>
> thanks,
> -- Shuah
>
>
>> 
>> 
>>>
>>> Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
>>> ---
>>>  drivers/gpu/drm/drm_probe_helper.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
>>> index ac953f0..6472b7f 100644
>>> --- a/drivers/gpu/drm/drm_probe_helper.c
>>> +++ b/drivers/gpu/drm/drm_probe_helper.c
>>> @@ -282,8 +282,8 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>>>  	dev->mode_config.poll_running = drm_kms_helper_poll;
>>>  
>>>  	if (connector->status == connector_status_disconnected) {
>>> -		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] disconnected\n",
>>> -			connector->base.id, connector->name);
>>> +		DRM_ERROR("[CONNECTOR:%d:%s] disconnected\n",
>>> +			  connector->base.id, connector->name);
>>>  		drm_mode_connector_update_edid_property(connector, NULL);
>>>  		verbose_prune = false;
>>>  		goto prune;
>> 
>

-- 
Jani Nikula, Intel Open Source Technology Center