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Message-ID: <c091da0b-a150-428a-bf96-75f9f3eab2e2@samsung.com>
Date: Wed, 17 Apr 2024 12:20:29 +0200
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Subject: Re: [PATCH 12/15] tty: serial: switch from circ_buf to kfifo
To: Anders Roxell <anders.roxell@linaro.org>, Jiri Slaby
	<jirislaby@kernel.org>
Cc: gregkh@linuxfoundation.org, linux-amlogic@lists.infradead.org,
	"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
	linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Bjorn Andersson
	<andersson@kernel.org>, Konrad Dybcio <konrad.dybcio@linaro.org>, Neil
	Armstrong <neil.armstrong@linaro.org>, Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>, Martin Blumenstingl
	<martin.blumenstingl@googlemail.com>
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From: Marek Szyprowski <m.szyprowski@samsung.com>
In-Reply-To: <Zh-fgtujwjiSXz7D@monster>
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References: <20240405060826.2521-1-jirislaby@kernel.org>
	<20240405060826.2521-13-jirislaby@kernel.org>
	<CGME20240415125847eucas1p2bc180c35f40f9c490c713679871af9ae@eucas1p2.samsung.com>
	<91ac609b-0fae-4856-a2a6-636908d7ad3c@samsung.com>
	<d70049d5-d0fe-465f-a558-45b6785f6014@kernel.org> <Zh-fgtujwjiSXz7D@monster>

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