linux-kernel - Re: Bogus video resolution in Linux 3.5-rc4

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Date:	Tue, 26 Jun 2012 09:21:16 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Sven Joachim <svenjoac@....de>
Cc:	dri-devel@...ts.freedesktop.org, Adam Jackson <ajax@...hat.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Dave Airlie <airlied@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: Bogus video resolution in Linux 3.5-rc4

At Mon, 25 Jun 2012 21:38:56 +0200,
Sven Joachim wrote:
> 
> Am 25.06.2012 um 21:24 schrieb Takashi Iwai:
> 
> >> > And, does the patch below help?
> >> 
> >> Somewhat: at least I get 1280x1024 again, but at 60 rather than 75 Hz.
> >
> > I guess it worked casually because 1280x1024@75 was the highest
> > resolution / rate, so it was picked up as the preferred mode...
> 
> Quite possible.  Problem is that 1280x1024@60 looks worse, so I'd like
> to get the 75 Hz back.
> 
> >> The xrandr command shows various bogus modes.
> >
> > Can't these values be displayed on your monitor at all?
> 
> It's a TFT LCD with 1280x1024 pixels.

Yes, but displaying higher resolutions wasn't too uncommon in the
earlier VGA days.  So, this doesn't mean the higher modes are
"bogus" as long they are in the range the monitor itself advertises.

On the second thought, if there are many such broken monitors, it
might be safer to exclude the inferred modes with higher resolutions.

The original problem was that the resolution like 1366x768 or 1600x900
doesn't appear in the mode list.  These are supposed to be lower than
the native.  Restricting the higher resolutions won't regress for
these problems.

The patch below is a quick fix.


Takashi

---
From: Takashi Iwai <tiwai@...e.de>
Subject: [PATCH] drm: edid: Don't add inferred modes with higher resolution

When a monitor EDID doesn't give the preferred bit, driver assumes
that the mode with the higest resolution and rate is the preferred
mode.  Meanwhile the recent changes for allowing more modes in the
GFT/CVT ranges give actually more modes, and some modes may be over
the native size.  Thus such a mode would be picked up as the preferred
mode although it's no native resolution.

For avoiding such a problem, this patch limits the addition of
inferred modes by checking not to be greater than other modes.
Also, it checks the duplicated mode entry at the same time.

Signed-off-by: Takashi Iwai <tiwai@...e.de>
---
 drivers/gpu/drm/drm_edid.c |   27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 5873e48..a8743c3 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1039,6 +1039,24 @@ mode_in_range(const struct drm_display_mode *mode, struct edid *edid,
 	return true;
 }
 
+static bool valid_inferred_mode(const struct drm_connector *connector,
+				const struct drm_display_mode *mode)
+{
+	struct drm_display_mode *m;
+	bool ok = false;
+
+	list_for_each_entry(m, &connector->probed_modes, head) {
+		if (mode->hdisplay == m->hdisplay &&
+		    mode->vdisplay == m->vdisplay &&
+		    drm_mode_vrefresh(mode) == drm_mode_vrefresh(m))
+			return false; /* duplicated */
+		if (mode->hdisplay <= m->hdisplay &&
+		    mode->vdisplay <= m->vdisplay)
+			ok = true;
+	}
+	return ok;
+}
+
 static int
 drm_dmt_modes_for_range(struct drm_connector *connector, struct edid *edid,
 			struct detailed_timing *timing)
@@ -1048,7 +1066,8 @@ drm_dmt_modes_for_range(struct drm_connector *connector, struct edid *edid,
 	struct drm_device *dev = connector->dev;
 
 	for (i = 0; i < drm_num_dmt_modes; i++) {
-		if (mode_in_range(drm_dmt_modes + i, edid, timing)) {
+		if (mode_in_range(drm_dmt_modes + i, edid, timing) &&
+		    valid_inferred_mode(connector, drm_dmt_modes + i)) {
 			newmode = drm_mode_duplicate(dev, &drm_dmt_modes[i]);
 			if (newmode) {
 				drm_mode_probed_add(connector, newmode);
@@ -1088,7 +1107,8 @@ drm_gtf_modes_for_range(struct drm_connector *connector, struct edid *edid,
 			return modes;
 
 		fixup_mode_1366x768(newmode);
-		if (!mode_in_range(newmode, edid, timing)) {
+		if (!mode_in_range(newmode, edid, timing) ||
+		    !valid_inferred_mode(connector, newmode)) {
 			drm_mode_destroy(dev, newmode);
 			continue;
 		}
@@ -1116,7 +1136,8 @@ drm_cvt_modes_for_range(struct drm_connector *connector, struct edid *edid,
 			return modes;
 
 		fixup_mode_1366x768(newmode);
-		if (!mode_in_range(newmode, edid, timing)) {
+		if (!mode_in_range(newmode, edid, timing) ||
+		    !valid_inferred_mode(connector, newmode)) {
 			drm_mode_destroy(dev, newmode);
 			continue;
 		}
-- 
1.7.10.4

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