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    Subject[PATCH 5.10 318/593] drm/rockchip: cdn-dp: fix sign extension on an int multiply for a u64 result
    Date
    From: Colin Ian King <colin.king@canonical.com>

    [ Upstream commit ce0cb93a5adb283f577cd4661f511047b5e39028 ]

    The variable bit_per_pix is a u8 and is promoted in the multiplication
    to an int type and then sign extended to a u64. If the result of the
    int multiplication is greater than 0x7fffffff then the upper 32 bits will
    be set to 1 as a result of the sign extension. Avoid this by casting
    tu_size_reg to u64 to avoid sign extension and also a potential overflow.

    Fixes: 1a0f7ed3abe2 ("drm/rockchip: cdn-dp: add cdn DP support for rk3399")
    Signed-off-by: Colin Ian King <colin.king@canonical.com>
    Reviewed-by: Guenter Roeck <groeck@chromium.org>
    Signed-off-by: Heiko Stuebner <heiko@sntech.de>
    Link: https://patchwork.freedesktop.org/patch/msgid/20200915162049.36434-1-colin.king@canonical.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/gpu/drm/rockchip/cdn-dp-reg.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/gpu/drm/rockchip/cdn-dp-reg.c b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
    index 9d2163ef4d6e..33fb4d05c506 100644
    --- a/drivers/gpu/drm/rockchip/cdn-dp-reg.c
    +++ b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
    @@ -658,7 +658,7 @@ int cdn_dp_config_video(struct cdn_dp_device *dp)
    */
    do {
    tu_size_reg += 2;
    - symbol = tu_size_reg * mode->clock * bit_per_pix;
    + symbol = (u64)tu_size_reg * mode->clock * bit_per_pix;
    do_div(symbol, dp->max_lanes * link_rate * 8);
    rem = do_div(symbol, 1000);
    if (tu_size_reg > 64) {
    --
    2.30.2


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