[PATCH] drm/ast: Return value when do not get edid

[Thomas Zimmermann]

Am 17.07.21 um 03:14 schrieb Ainux Wang:
> Thomas Zimmermann <tzimmermann at suse.de> 于2021年7月16日周五 下午8:00写道：
>>
>> Hi
>>
>> Am 16.07.21 um 11:55 schrieb ainux.wang at gmail.com:
>>> From: "Ainux.Wang" <ainux.wang at gmail.com>
>>>
>>> There is should a status when do not get edid.
>>
>> Well, not really.
>>
>> So, the problem is that VGA is not hotplug-able. It's supposed to be
>> connected when the computer gets switched on. And there's no interface
>> for sensing the connection state.
>>
>> But in practice, the cable can be attached/detached at any time. Reading
>> out the EDID is the non-official way for detecting the connection state.
>> You either get EDID data or garbage, where the latter is interpreted as
>> 'disconnected'.
>>
>> But really old monitors (maybe mid-90s and before) don't provide EDID
>> data. For those, DRM adds standard VGA modes IIRC. And they would likely
>> be detected as 'disconnected'.
>>
>> I'll merge your original patch '(r <= 0)' and anyone who's stuck with
>> such an old monitor can probably specify a compatible EDID on the kernel
>> command line.
>>
>> (I'd like to hear other people's opinion about this TBH.)
>>
>> Best regards
>> Thomas
>>
> Hi，
> Thank you for your review and reply, and what is the ‘IIRC’, i do not

IIRC stands for 'if I remember correctly'

> find it in the
> kernel document.
> 
> Best regards
> Ainux
>>>
>>> Signed-off-by: Ainux.Wang <ainux.wang at gmail.com>
>>> ---
>>>    drivers/gpu/drm/ast/ast_mode.c | 4 +++-
>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
>>> index e5996ae03c49..05df48b3d223 100644
>>> --- a/drivers/gpu/drm/ast/ast_mode.c
>>> +++ b/drivers/gpu/drm/ast/ast_mode.c
>>> @@ -1231,8 +1231,10 @@ static int ast_get_modes(struct drm_connector *connector)
>>>                ret = drm_add_edid_modes(connector, edid);
>>>                kfree(edid);
>>>                return ret;
>>> -     } else
>>> +     } else {
>>>                drm_connector_update_edid_property(&ast_connector->base, NULL);
>>> +             return -ENXIO;
>>> +     }
>>>        return 0;
>>>    }
>>>
>>>
>>
>> --
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Maxfeldstr. 5, 90409 Nürnberg, Germany
>> (HRB 36809, AG Nürnberg)
>> Geschäftsführer: Felix Imendörffer
>>

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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