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serial: qcom_geni: Fix RX DMA stall when SE_DMA_RX_LEN_IN is zero

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In qcom_geni_serial_handle_rx_dma(), geni_se_rx_dma_unprep() clears
port->rx_dma_addr before SE_DMA_RX_LEN_IN is read. If the register is zero,
for example when the RX stale counter fires on an idle line, the handler
returns without calling geni_se_rx_dma_prep().

The next RX DMA interrupt then hits the !port->rx_dma_addr guard and
returns immediately, so the RX DMA buffer is never rearmed and later input
is lost.

Keep the handler on the rearm path when rx_in is zero. Warn about the
unexpected zero-length DMA completion, skip received-data handling, and
always call geni_se_rx_dma_prep().

Fixes: 2aaa43c707 ("tty: serial: qcom-geni-serial: add support for serial engine DMA")
Cc: stable@vger.kernel.org
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Viken Dadhaniya <viken.dadhaniya@oss.qualcomm.com>
Link: https://patch.msgid.link/20260528-serial-rx-0-byte-fix-v2-1-b4195cfe342f@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Viken Dadhaniya 2026-05-28 22:48:07 +05:30 committed by Greg Kroah-Hartman
parent b586d69177
commit b93062b6d8
1 changed files with 3 additions and 6 deletions
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9
drivers/tty/serial/qcom_geni_serial.c
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@ -905,12 +905,9 @@ static void qcom_geni_serial_handle_rx_dma(struct uart_port *uport, bool drop)
port->rx_dma_addr = 0;
rx_in = readl(uport->membase + SE_DMA_RX_LEN_IN);
if (!rx_in) {
dev_warn(uport->dev, "serial engine reports 0 RX bytes in!\n");
return;
}
if (!drop)
if (!rx_in)
dev_warn_ratelimited(uport->dev, "serial engine reports 0 RX bytes in!\n");
else if (!drop)
handle_rx_uart(uport, rx_in);
ret = geni_se_rx_dma_prep(&port->se, port->rx_buf,