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    Subject[PATCH AUTOSEL 5.7 138/274] drm/bridge: fix stack usage warning on old gcc
    Date
    From: Arnd Bergmann <arnd@arndb.de>

    [ Upstream commit 78b0d99a68ecdc84728c99f4fef71942e9ecf35a ]

    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
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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)
    --
    2.25.1
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