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

[Thomas Zimmermann]

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

> 
> 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

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