Re: [PATCH] imx_serial: set wake bit when we receive a data byte

[Philippe Mathieu-Daudé]

Hi Martin,

On 8/6/23 17:41, Martin Kaiser wrote:
> The linux kernel added a flood check for rx data recently in commmit
> 496a4471b7c3 ("serial: imx: work-around for hardware RX flood"). This
> check uses the wake bit in the uart status register 2. The wake bit
> indicates that the receiver detected a start bit. If the kernel sees a
> number of rx interrupts without the wake bit being set, it treats this as
> spurious data and resets the uart port. imx_serial does never set the
> wake bit and triggers the kernel's flood check.
>
> This patch adds support for the wake bit. wake is set when we receive a
> new character (it's not set for break events). It seems that wake is
> cleared by the kernel driver, the hardware does not have to clear it
> automatically after data was read.
>
> Signed-off-by: Martin Kaiser <martin@kaiser.cx>
> ---
>   hw/char/imx_serial.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/hw/char/imx_serial.c b/hw/char/imx_serial.c
> index ee1375e26d..44125d5f47 100644
> --- a/hw/char/imx_serial.c
> +++ b/hw/char/imx_serial.c
> @@ -321,6 +321,9 @@ static void imx_put_data(void *opaque, uint32_t value)
>   
>   static void imx_receive(void *opaque, const uint8_t *buf, int size)
>   {
> +    IMXSerialState *s = (IMXSerialState *)opaque;
> +
> +    s->usr2 |= USR2_WAKE;
>       imx_put_data(opaque, *buf);
>   }
>   

Shouldn't we mask this bit for interruptions now?

-- >8 --
diff --git a/include/hw/char/imx_serial.h b/include/hw/char/imx_serial.h
index 91c9894ad5..b823f94519 100644
--- a/include/hw/char/imx_serial.h
+++ b/include/hw/char/imx_serial.h
@@ -71,6 +71,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(IMXSerialState, IMX_SERIAL)

 #define UCR4_DREN       BIT(0)    /* Receive Data Ready interrupt 
enable */
 #define UCR4_TCEN       BIT(3)    /* TX complete interrupt enable */
+#define UCR4_WKEN       BIT(7)    /* WAKE interrupt enable */

 #define UTS1_TXEMPTY    (1<<6)
 #define UTS1_RXEMPTY    (1<<5)
diff --git a/hw/char/imx_serial.c b/hw/char/imx_serial.c
index ee1375e26d..c8ec247350 100644
--- a/hw/char/imx_serial.c
+++ b/hw/char/imx_serial.c
@@ -80,7 +80,7 @@ static void imx_update(IMXSerialState *s)
      * TCEN and TXDC are both bit 3
      * RDR and DREN are both bit 0
      */
-    mask |= s->ucr4 & (UCR4_TCEN | UCR4_DREN);
+    mask |= s->ucr4 & (UCR4_WKEN | UCR4_TCEN | UCR4_DREN);

     usr2 = s->usr2 & mask;
---