Re: [PATCH 12/15] tty: serial: switch from circ_buf to kfifo

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On 15. 04. 24, 14:58, Marek Szyprowski wrote:
Dear All,

On 05.04.2024 08:08, Jiri Slaby (SUSE) wrote:
Switch from struct circ_buf to proper kfifo. kfifo provides much better
API, esp. when wrap-around of the buffer needs to be taken into account.
Look at pl011_dma_tx_refill() or cpm_uart_tx_pump() changes for example.

Kfifo API can also fill in scatter-gather DMA structures, so it easier
for that use case too. Look at lpuart_dma_tx() for example. Note that
not all drivers can be converted to that (like atmel_serial), they
handle DMA specially.

Note that usb-serial uses kfifo for TX for ages.

omap needed a bit more care as it needs to put a char into FIFO to start
the DMA transfer when OMAP_DMA_TX_KICK is set. In that case, we have to
do kfifo_dma_out_prepare twice: once to find out the tx_size (to find
out if it is worths to do DMA at all -- size >= 4), the second time for
the actual transfer.

All traces of circ_buf are removed from serial_core.h (and its struct

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@xxxxxxxxxx>

This patch landed in linux-next as commit 1788cf6a91d9 ("tty: serial:
switch from circ_buf to kfifo"). Unfortunately it breaks UART operation
on thr Amlogic Meson based boards (drivers/tty/serial/meson_uart.c
driver) and Qualcomm RB5 board (drivers/tty/serial/qcom_geni_serial.c).
Once the init process is started, a complete garbage is printed to the
serial console. Here is an example how it looks:

Oh my!

Both drivers move the tail using both kfifo and uart_xmit_advance() interfaces. Bah. Does it help to remove that uart_xmit_advance() for both of them? (TX stats will be broken.)

Users of uart_port_tx() are not affected.

This is my fault when merging uart_xmit_advance() with this series.

suse labs

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