linux-kernel - Re: [PATCHv2] drm: fb_helper: prefer to use mode, which is not DRM_MODE_TYPE

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Date:	Mon, 20 Apr 2015 10:09:29 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Radek Dostal <rd@...ekdostal.com>
Cc:	airlied@...ux.ie, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] drm: fb_helper: prefer to use mode, which is not
 DRM_MODE_TYPE_USERDEF

On Mon, Apr 20, 2015 at 07:26:33AM +0200, Radek Dostal wrote:
> commit eaf99c749d43 ("drm: Perform cmdline mode parsing during connector
> initialisation") breaks HDMI output on BeagleBone Black with LG TV
> (model 19LS4R-ZA) when "video=HDMI-A-1:1280x720@60" is specified on
> the command line.
> 
> The reason is newly added mode
> '"1280x720" 60 74440 1280 1336 1472 1664 720 721 724 746 0x20 0x6'
> , which is added by function drm_helper_probe_add_cmdline_mode (introduced
> in above mentioned commit). This mode causes TV to go black and show "No
> signal" message.
> 
> When cmdline_mode is set, it is preferred to use matching mode obtained
> from EDID, than mode calculated by function
> drm_mode_create_from_cmdline_mode

The EDID modes should be earlier in the list, and so higher priority
than the cmdline mode. The only instance I see that breaking down is if
the mode gets created by drm_pick_cmdline_mode, i.e.

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index cac422916c7a..d55c2de6a99f 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1327,7 +1327,7 @@ again:
 create_mode:
        mode = drm_mode_create_from_cmdline_mode(fb_helper_conn->connector->dev,
                                                 cmdline_mode);
-       list_add(&mode->head, &fb_helper_conn->connector->modes);
+       list_add_tail(&mode->head, &fb_helper_conn->connector->modes);
        return mode;
 }
 EXPORT_SYMBOL(drm_pick_cmdline_mode);

Can you please print the matching modes and trace where the userdef mode
gets added before the EDID modes?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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