linux-kernel - [PATCH 6/7] mxser: don't read from UART

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Message-Id: <20210922075938.31390-6-jslaby@suse.cz>
Date:   Wed, 22 Sep 2021 09:59:37 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     gregkh@...uxfoundation.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 6/7] mxser: don't read from UART_FCR

The UART_FCR register is write-only. When reading it, one gets contents
of (read-only) UART_IIR instead as they are shared. This mistake was
performed in mxser_flush_buffer() to clear FIFOs.

Actually FCR handling throughout the driver is completely broken. On
many places, it respects neither mu860 settings, nor FIFO (16450 vs
16550) setting. This patch doesn't help to fix this, it actually does
the same. We will introduce a mxser_port::FCR in the next patch to fix
this issue.

Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/tty/mxser.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/tty/mxser.c b/drivers/tty/mxser.c
index 6913a1caa6f0..4ce21cdb1ea5 100644
--- a/drivers/tty/mxser.c
+++ b/drivers/tty/mxser.c
@@ -859,17 +859,14 @@ static int mxser_open(struct tty_struct *tty, struct file *filp)
 static void mxser_flush_buffer(struct tty_struct *tty)
 {
 	struct mxser_port *info = tty->driver_data;
-	char fcr;
 	unsigned long flags;
 
 
 	spin_lock_irqsave(&info->slock, flags);
 	info->xmit_cnt = info->xmit_head = info->xmit_tail = 0;
 
-	fcr = inb(info->ioaddr + UART_FCR);
-	outb((fcr | UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT),
+	outb(UART_FCR_ENABLE_FIFO | UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT,
 		info->ioaddr + UART_FCR);
-	outb(fcr, info->ioaddr + UART_FCR);
 
 	spin_unlock_irqrestore(&info->slock, flags);
 
-- 
2.33.0