-----Original Message-----
From: linux-tegra-owner@vger.kernel.org <linux-tegra-
owner@vger.kernel.org> On Behalf Of Thierry Reding
Sent: Tuesday, August 13, 2019 3:12 PM
To: Krishna Yarlagadda <redacted>
Cc: gregkh@linuxfoundation.org; robh+dt@kernel.org;
mark.rutland@arm.com; Jonathan Hunter [off-list ref]; Laxman
Dewangan [off-list ref]; jslaby@suse.com; linux-
serial@vger.kernel.org; devicetree@vger.kernel.org; linux-
tegra@vger.kernel.org; linux-kernel@vger.kernel.org; Shardar Mohammed
[off-list ref]
Subject: Re: [PATCH 02/14] serial: tegra: add support to ignore read

On Mon, Aug 12, 2019 at 04:58:11PM +0530, Krishna Yarlagadda wrote:

quoted

From: Shardar Shariff Md <redacted>

Add support to ignore read characters if CREAD flag is not set.

Signed-off-by: Shardar Shariff Md <redacted>
Signed-off-by: Krishna Yarlagadda <redacted>
---
 drivers/tty/serial/serial-tegra.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/tty/serial/serial-tegra.c

b/drivers/tty/serial/serial-tegra.c
index 19f4c24..93d299e 100644

--- a/drivers/tty/serial/serial-tegra.c
+++ b/drivers/tty/serial/serial-tegra.c

@@ -542,6 +542,9 @@ static void tegra_uart_handle_rx_pio(struct

tegra_uart_port *tup,

quoted

 		ch = (unsigned char) tegra_uart_read(tup, UART_RX);
 		tup->uport.icount.rx++;

+		if (tup->uport.ignore_status_mask & UART_LSR_DR)
+			continue;
+
 		if (!uart_handle_sysrq_char(&tup->uport, ch) && tty)
 			tty_insert_flip_char(tty, ch, flag);

Is it a good idea to ignore even sysrq characters if CREAD is not set?
According to termios, CREAD enables the receiver, so technically if it isn't set
you can't even receive sysrq characters. But I don't know if there are any
rules regarding this.

Is this the same way that other drivers work?

Thierry

Looked into few drivers and sysrq characters are not ignored. This driver does
not support console driver. So this might not be needed.

KY

quoted

 	} while (1);

@@ -562,6 +565,10 @@ static void tegra_uart_copy_rx_to_tty(struct

tegra_uart_port *tup,

quoted

 		dev_err(tup->uport.dev, "No tty port\n");
 		return;
 	}
+
+	if (tup->uport.ignore_status_mask & UART_LSR_DR)
+		return;
+
 	dma_sync_single_for_cpu(tup->uport.dev, tup->rx_dma_buf_phys,
 				TEGRA_UART_RX_DMA_BUFFER_SIZE,

DMA_FROM_DEVICE);

quoted

 	copied = tty_insert_flip_string(tty, @@ -1190,6 +1197,11 @@ static
void tegra_uart_set_termios(struct uart_port *u,
 	tegra_uart_write(tup, tup->ier_shadow, UART_IER);
 	tegra_uart_read(tup, UART_IER);

+	tup->uport.ignore_status_mask = 0;
+	/* Ignore all characters if CREAD is not set */
+	if ((termios->c_cflag & CREAD) == 0)
+		tup->uport.ignore_status_mask |= UART_LSR_DR;
+
 	spin_unlock_irqrestore(&u->lock, flags);  }

--
2.7.4