This is a note to let you know that I've just added the patch titled

serial: 8250: Fall back to non-DMA Rx if IIR_RDI occurs

to my tty git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git in the tty-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From a931237cbea256aff13bb403da13a97b2d1605d9 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= ilpo.jarvinen@linux.intel.com Date: Tue, 8 Nov 2022 14:19:49 +0200 Subject: serial: 8250: Fall back to non-DMA Rx if IIR_RDI occurs MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

DW UART sometimes triggers IIR_RDI during DMA Rx when IIR_RX_TIMEOUT should have been triggered instead. Since IIR_RDI has higher priority than IIR_RX_TIMEOUT, this causes the Rx to hang into interrupt loop. The problem seems to occur at least with some combinations of small-sized transfers (I've reproduced the problem on Elkhart Lake PSE UARTs).

If there's already an on-going Rx DMA and IIR_RDI triggers, fall graciously back to non-DMA Rx. That is, behave as if IIR_RX_TIMEOUT had occurred.

8250_omap already considers IIR_RDI similar to this change so its nothing unheard of.

Fixes: 75df022b5f89 ("serial: 8250_dma: Fix RX handling") Cc: stable@vger.kernel.org Co-developed-by: Srikanth Thokala srikanth.thokala@intel.com Signed-off-by: Srikanth Thokala srikanth.thokala@intel.com Co-developed-by: Aman Kumar aman.kumar@intel.com Signed-off-by: Aman Kumar aman.kumar@intel.com Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Link: https://lore.kernel.org/r/20221108121952.5497-2-ilpo.jarvinen@linux.intel.co... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/8250/8250_port.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index fe8662cd9402..92dd18716169 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1897,6 +1897,10 @@ EXPORT_SYMBOL_GPL(serial8250_modem_status); static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir) { switch (iir & 0x3f) { + case UART_IIR_RDI: + if (!up->dma->rx_running) + break; + fallthrough; case UART_IIR_RX_TIMEOUT: serial8250_rx_dma_flush(up); fallthrough;