linux-kernel - [PATCH] drm/bridge: fix stack usage warning on old gcc

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Date:   Tue, 28 Apr 2020 23:53:54 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/bridge: fix stack usage warning on old gcc

Some older versions of gcc badly optimize code that passes
an inline function argument into another function by reference,
causing huge stack usage:

drivers/gpu/drm/bridge/tc358768.c: In function 'tc358768_bridge_pre_enable':
drivers/gpu/drm/bridge/tc358768.c:840:1: error: the frame size of 2256 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]

Use a temporary variable as a workaround and add a comment pointing
to the gcc bug.

Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/bridge/tc358768.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
index 1b39e8d37834..6650fe4cfc20 100644
--- a/drivers/gpu/drm/bridge/tc358768.c
+++ b/drivers/gpu/drm/bridge/tc358768.c
@@ -178,6 +178,8 @@ static int tc358768_clear_error(struct tc358768_priv *priv)
 
 static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)
 {
+	/* work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 */
+	int tmpval = val;
 	size_t count = 2;
 
 	if (priv->error)
@@ -187,7 +189,7 @@ static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)
 	if (reg < 0x100 || reg >= 0x600)
 		count = 1;
 
-	priv->error = regmap_bulk_write(priv->regmap, reg, &val, count);
+	priv->error = regmap_bulk_write(priv->regmap, reg, &tmpval, count);
 }
 
 static void tc358768_read(struct tc358768_priv *priv, u32 reg, u32 *val)
-- 
2.26.0