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mxser: don't read from UART_FCR

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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@suse.cz>
Link: https://lore.kernel.org/r/20210922075938.31390-6-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jiri Slaby 2021-09-22 09:59:37 +02:00 committed by Greg Kroah-Hartman
parent ee7e5e66f2
commit 215fa41c2d
1 changed files with 1 additions and 4 deletions
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5
drivers/tty/mxser.c
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@ -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);