serial: 8250_lpss: Use 16B DMA burst with Elkhart Lake

commit 7090abd6ad0610a144523ce4ffcb8560909bf2a8 upstream.

Configure DMA to use 16B burst size with Elkhart Lake. This makes the
bus use more efficient and works around an issue which occurs with the
previously used 1B.

The fix was initially developed by Srikanth Thokala and Aman Kumar.
This together with the previous config change is the cleaned up version
of the original fix.

Fixes: 0a9410b981e9 ("serial: 8250_lpss: Enable DMA on Intel Elkhart Lake")
Cc: <stable@vger.kernel.org> # serial: 8250_lpss: Configure DMA also w/o DMA filter
Reported-by: Wentong Wu <wentong.wu@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20221108121952.5497-4-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_lpss.c b/drivers/tty/serial/8250/8250_lpss.c
index faa4251..87d70e8 100644 (file)
--- a/drivers/tty/serial/8250/8250_lpss.c
+++ b/drivers/tty/serial/8250/8250_lpss.c
@@ -177,6 +177,9 @@ static int ehl_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
         * matching with the registered General Purpose DMA controllers.
         */
        up->dma = dma;
+
+       lpss->dma_maxburst = 16;
+
        return 0;
 }