From: Thomas Zimmermann <tzimmermann@suse.de>
To: ainux.wang@gmail.com, airlied@redhat.com, airlied@linux.ie,
daniel@ffwll.ch
Cc: sterlingteng@gmail.com, chenhuacai@kernel.org,
dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/ast: Return value when do not get edid
Date: Fri, 16 Jul 2021 14:00:19 +0200 [thread overview]
Message-ID: <227ae846-c8a4-876a-2d4b-363aec33eca9@suse.de> (raw)
In-Reply-To: <20210716095522.27187-1-ainux.wang@gmail.com>
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Hi
Am 16.07.21 um 11:55 schrieb ainux.wang@gmail.com:
> From: "Ainux.Wang" <ainux.wang@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@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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next prev parent reply other threads:[~2021-07-16 12:00 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-16 9:55 [PATCH] drm/ast: Return value when do not get edid ainux.wang
2021-07-16 12:00 ` Thomas Zimmermann [this message]
2021-07-17 1:14 ` Ainux Wang
2021-07-20 9:09 ` Thomas Zimmermann
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