Regression: serial: imx: overrun errors on debug UART

[Stefan Wahren]

Hi Fabio,

Am 24.03.23 um 16:00 schrieb Stefan Wahren:
> Hi Fabio,
> 
> Am 24.03.23 um 13:57 schrieb Fabio Estevam:
>> Hi Stefan,
>>
>> On Fri, Mar 24, 2023 at 8:48 AM Ilpo Järvinen
>> <ilpo.jarvinen at linux.intel.com> wrote:
>>
>>> This has come up earlier, see e.g.:
>>>
>>> https://lore.kernel.org/linux-serial/20221003110850.GA28338@francesco-nb.int.toradex.com/
>>>
>>> My somewhat uninformed suggestion: if the overrun problems mostly 
>>> show up
>>> with console ports, maybe the trigger level could depend on the port
>>> being a console or not?
>> Does the change below help? Taking Ilpo's suggestion into account:
> this breaks the boot / debug console completely, but i got the idea.
>>

based on your patch, i successfully tested this:

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index f07c4f9ff13c..1aacaa637ede 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1277,6 +1277,7 @@ static void imx_uart_clear_rx_errors(struct 
imx_port *sport)
  }

  #define TXTL_DEFAULT 2 /* reset default */
+#define RXTL_DEFAULT_CONSOLE 1 /* reset default */
  #define RXTL_DEFAULT 8 /* 8 characters or aging timer */
  #define TXTL_DMA 8 /* DMA burst setting */
  #define RXTL_DMA 9 /* DMA burst setting */
@@ -1286,6 +1287,9 @@ static void imx_uart_setup_ufcr(struct imx_port 
*sport,
  {
  	unsigned int val;

+	if (uart_console(&sport->port))
+		rxwl = RXTL_DEFAULT_CONSOLE; // fallback
+
  	/* set receiver / transmitter trigger level */
  	val = imx_uart_readl(sport, UFCR) & (UFCR_RFDIV | UFCR_DCEDTE);
  	val |= txwl << UFCR_TXTL_SHF | rxwl;