[PATCH] drm/fb-helper: Fix of-by-one in setcmap_pseudo_palette

[Daniel Vetter <daniel.vetter@ffwll.ch>]

[Fair warning: This is pure conjecture right now.]

In

commit b8e2b0199cc377617dc238f5106352c06dcd3fa2
Author: Peter Rosin <peda@axentia.se>
Date:   Tue Jul 4 12:36:57 2017 +0200

    drm/fb-helper: factor out pseudo-palette

Peter extracted the pseudo palette computation, but seems to have done
an off-by-one. I spotted that +1, but then noticed that we've passed
start++ to (now gone) setcolreg function, so it seemed to all match
up. Except post vs. pre-increment ftw.

Result is that the palette is off-by-one, and the forground color
(slot 0) ends up black, rendering a fairly unreadable console.

What baffles me is that on some systems it still seems to work
somehow, which lead us all down a wild goose chase trying to add
load_lut calls back in in various places (which was also intentionally
removed, but really doesn't seem to be the real root cause).

Fixes: b8e2b0199cc3 ("drm/fb-helper: factor out pseudo-palette")
Cc: Peter Rosin <peda@axenita.se>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v4.14+
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=198123
Reported-by: Deposite Pirate <dpirate@metalpunks.info>
Reported-by: Bill Fraser <bill.fraser@gmail.com>
Cc: Deposite Pirate <dpirate@metalpunks.info>
Cc: Bill Fraser <bill.fraser@gmail.com>
Cc: Michel Dänzer <michel@daenzer.net>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 035784ddd133..1c3a200c4a10 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1295,7 +1295,7 @@ static int setcmap_pseudo_palette(struct fb_cmap *cmap, struct fb_info *info)
 			mask <<= info->var.transp.offset;
 			value |= mask;
 		}
-		palette[cmap->start + i] = value;
+		palette[cmap->start] = value;
 	}
 
 	return 0;
-- 
2.15.1