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 the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: serial-8250-fall-back-to-non-dma-rx-if-iir_rdi-occurs.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From a931237cbea256aff13bb403da13a97b2d1605d9 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@xxxxxxxxxxxxxxx> 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 From: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> commit a931237cbea256aff13bb403da13a97b2d1605d9 upstream. 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@xxxxxxxxxxxxxxx> Co-developed-by: Srikanth Thokala <srikanth.thokala@xxxxxxxxx> Signed-off-by: Srikanth Thokala <srikanth.thokala@xxxxxxxxx> Co-developed-by: Aman Kumar <aman.kumar@xxxxxxxxx> Signed-off-by: Aman Kumar <aman.kumar@xxxxxxxxx> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20221108121952.5497-2-ilpo.jarvinen@xxxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/tty/serial/8250/8250_port.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1865,6 +1865,10 @@ EXPORT_SYMBOL_GPL(serial8250_modem_statu 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; + /* fall-through */ case UART_IIR_RX_TIMEOUT: serial8250_rx_dma_flush(up); /* fall-through */ Patches currently in stable-queue which might be from ilpo.jarvinen@xxxxxxxxxxxxxxx are queue-4.19/serial-8250_lpss-configure-dma-also-w-o-dma-filter.patch queue-4.19/serial-8250-fall-back-to-non-dma-rx-if-iir_rdi-occurs.patch queue-4.19/serial-8250_omap-remove-wait-loop-from-errata-i202-w.patch