RE: [EXT] Re: [PATCH V2 1/1] serial: fsl_lpuart: zero out parity bit in CS7 mode

-----Original Message----- From: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Sent: Tuesday, July 19, 2022 5:26 AM To: Shenwei Wang shenwei.wang@nxp.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org; linux-serial <linux- serial@vger.kernel.org>; stable@vger.kernel.org Subject: [EXT] Re: [PATCH V2 1/1] serial: fsl_lpuart: zero out parity bit in CS7 mode

Caution: EXT Email

On Thu, 14 Jul 2022, Shenwei Wang wrote:

...

The LPUART hardware doesn't zero out the parity bit on the received characters. This behavior won't impact the use cases of CS8 because the parity bit is the 9th bit which is not currently used by software. But the parity bit for CS7 must be zeroed out by software in order to get the correct raw data.

This problem only occurs with the lpuart32 variant? Or should the other functions be changed as well?

In theory this problem should occur with the non lpuart32 variant too, because LPUART32 was derived from the non lpuart32 IP module. However, I don't have a platform to confirm it.

Thanks, Shenwei

-- i.

...

Signed-off-by: Shenwei Wang shenwei.wang@nxp.com

changes in v2

• remove the "inline" keyword from the function of

lpuart_tty_insert_flip_string;

changes in v1

• fix the code indent and whitespace issue;

drivers/tty/serial/fsl_lpuart.c | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index fc7d235a1e270..afa0f941c862f 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -274,6 +274,8 @@ struct lpuart_port { int rx_dma_rng_buf_len; unsigned int dma_tx_nents; wait_queue_head_t dma_wait;

• bool                    is_cs7; /* Set to true when character size is 7 */
  

•                                 /* and the parity is enabled            */
  

};

struct lpuart_soc_data { @@ -1022,6 +1024,9 @@ static void lpuart32_rxint(struct lpuart_port *sport) flg = TTY_OVERRUN; }

•         if (sport->is_cs7)
  

•                 rx &= 0x7F;
  

•         if (tty_insert_flip_char(port, rx, flg) == 0)
                  sport->port.icount.buf_overrun++;
  }
  

@@ -1107,6 +1112,17 @@ static void lpuart_handle_sysrq(struct lpuart_port

*sport)

...

  }

}

+static int lpuart_tty_insert_flip_string(struct tty_port *port,

• unsigned char *chars, size_t size, bool is_cs7) {
  

• int i;
  

• if (is_cs7)
  

•         for (i = 0; i < size; i++)
  

•                 chars[i] &= 0x7F;
  

• return tty_insert_flip_string(port, chars, size); }
  

static void lpuart_copy_rx_to_tty(struct lpuart_port *sport) { struct tty_port *port = &sport->port.state->port; @@ -1217,7 +1233,8 @@ static void lpuart_copy_rx_to_tty(struct lpuart_port *sport) if (ring->head < ring->tail) { count = sport->rx_sgl.length - ring->tail;

•         copied = tty_insert_flip_string(port, ring->buf + ring->tail, count);
  

•         copied = lpuart_tty_insert_flip_string(port, ring->buf + ring->tail,
  

•                                 count, sport->is_cs7);
          if (copied != count)
                  sport->port.icount.buf_overrun++;
          ring->tail = 0;
  

@@ -1227,7 +1244,8 @@ static void lpuart_copy_rx_to_tty(struct lpuart_port

*sport)

...

  /* Finally we read data from tail to head */
  if (ring->tail < ring->head) {
          count = ring->head - ring->tail;

•         copied = tty_insert_flip_string(port, ring->buf + ring->tail, count);
  

•         copied = lpuart_tty_insert_flip_string(port, ring->buf + ring->tail,
  

•                                 count, sport->is_cs7);
          if (copied != count)
                  sport->port.icount.buf_overrun++;
          /* Wrap ring->head if needed */ @@ -2066,6 +2084,7 @@
  

lpuart32_set_termios(struct uart_port *port, struct ktermios *termios, ctrl = old_ctrl = lpuart32_read(&sport->port, UARTCTRL); bd = lpuart32_read(&sport->port, UARTBAUD); modem = lpuart32_read(&sport->port, UARTMODIR);

• sport->is_cs7 = false;
  /*
   * only support CS8 and CS7, and for CS7 must enable PE.
   * supported mode:
  

@@ -2184,6 +2203,9 @@ lpuart32_set_termios(struct uart_port *port, struct

ktermios *termios,

...

  lpuart32_write(&sport->port, ctrl, UARTCTRL);
  /* restore control register */

• if ((ctrl & (UARTCTRL_PE | UARTCTRL_M)) == UARTCTRL_PE)
  

•         sport->is_cs7 = true;
  

• if (old && sport->lpuart_dma_rx_use) {
          if (!lpuart_start_rx_dma(sport))
                  rx_dma_timer_init(sport);
  

-- 2.25.1