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serial: sh-sci: Check that the DMA cookie is valid

The driver updates struct sci_port::tx_cookie to zero right before the TX
work is scheduled, or to -EINVAL when DMA is disabled.
dma_async_is_complete(), called through dma_cookie_status() (and possibly
through dmaengine_tx_status()), considers cookies valid only if they have
values greater than or equal to 1.

Passing zero or -EINVAL to dmaengine_tx_status() before any TX DMA
transfer has started leads to an incorrect TX status being reported, as the
cookie is invalid for the DMA subsystem. This may cause long wait times
when the serial device is opened for configuration before any TX activity
has occurred.

Check that the TX cookie is valid before passing it to
dmaengine_tx_status().

Fixes: 7cc0e0a43a91 ("serial: sh-sci: Check if TX data was written to device in .tx_empty()")
Cc: stable <stable@kernel.org>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Link: https://patch.msgid.link/20251217135759.402015-1-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

authored by

Claudiu Beznea and committed by
Greg Kroah-Hartman c3ca8a0a f5415114

+1 -1
+1 -1
drivers/tty/serial/sh-sci.c
··· 1914 1914 struct dma_tx_state state; 1915 1915 enum dma_status status; 1916 1916 1917 - if (!s->chan_tx) 1917 + if (!s->chan_tx || s->cookie_tx <= 0) 1918 1918 return; 1919 1919 1920 1920 status = dmaengine_tx_status(s->chan_tx, s->cookie_tx, &state);