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@arndb.de>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200428215408.4111675-1-arnd@arndb.de

diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
index 1b39e8d..6650fe4 100644 (file)
--- 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)