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

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 17.04.2024 12:08, Anders Roxell wrote:
> On 2024-04-15 15:28, Jiri Slaby wrote:
>> On 15. 04. 24, 14:58, Marek Szyprowski wrote:
>>> 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
>>>> uart_state).
>>>>
>>>> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
>>>> ...
>>> 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.
>>
> I'm trying to run on two dragonboard devices db410c and db845c and both
> fails to boot see the boot failure from db845c [1], linux-next tag: next-20240415.
> I tried to apply the patch [2] (that you proposed in this thread) ontop of next-20240415. However, that didn't
> help bootlog on db845c [3].

This is a different issue, which I've reported 2 days ago. See the 
following thread:

https://lore.kernel.org/all/d3eb9f21-f3e1-43ec-bf41-984c6aa5cfc8@samsung.com/


Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland