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    Subject[PATCH 4.14 78/89] udlfb: set optimal write delay
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mikulas Patocka <mpatocka@redhat.com>

    commit bb24153a3f13dd0dbc1f8055ad97fe346d598f66 upstream.

    The default delay 5 jiffies is too much when the kernel is compiled with
    HZ=100 - it results in jumpy cursor in Xwindow.

    In order to find out the optimal delay, I benchmarked the driver on
    1280x720x30fps video. I found out that with HZ=1000, 10ms is acceptable,
    but with HZ=250 or HZ=300, we need 4ms, so that the video is played
    without any frame skips.

    This patch changes the delay to this value.

    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    include/video/udlfb.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/include/video/udlfb.h
    +++ b/include/video/udlfb.h
    @@ -88,7 +88,7 @@ struct dlfb_data {
    #define MIN_RAW_PIX_BYTES 2
    #define MIN_RAW_CMD_BYTES (RAW_HEADER_BYTES + MIN_RAW_PIX_BYTES)

    -#define DL_DEFIO_WRITE_DELAY 5 /* fb_deferred_io.delay in jiffies */
    +#define DL_DEFIO_WRITE_DELAY msecs_to_jiffies(HZ <= 300 ? 4 : 10) /* optimal value for 720p video */
    #define DL_DEFIO_WRITE_DISABLE (HZ*60) /* "disable" with long delay */

    /* remove these once align.h patch is taken into kernel */

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