linux-kernel - Re: [PATCH 12/15] tty: serial: switch from circ

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Message-ID: <Zh-fgtujwjiSXz7D@monster>
Date: Wed, 17 Apr 2024 12:08:02 +0200
From: Anders Roxell <anders.roxell@...aro.org>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>, gregkh@...uxfoundation.org,
	linux-amlogic@...ts.infradead.org,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Kevin Hilman <khilman@...libre.com>,
	Jerome Brunet <jbrunet@...libre.com>,
	Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH 12/15] tty: serial: switch from circ_buf to kfifo

On 2024-04-15 15:28, Jiri Slaby wrote:
> 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
> > > uart_state).
> > > 
> > > Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.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].

Cheers,
Anders
[1] https://tuxapi.tuxsuite.com/v1/groups/linaro/projects/lkft/tests/2f7sLxYtIQXQzsnTzE1Dye2xweg/logs?format=html
[2] https://lore.kernel.org/lkml/20240416054825.6211-1-jirislaby@kernel.org/raw
[3] https://tuxapi.tuxsuite.com/v1/groups/linaro/projects/anders/tests/2fDgvWnyEmFm9mqMCxOaruBOfTe/logs?format=html