linux-kernel - Re: [PATCH v6 0/2] usb: serial: add support for CH348

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Date:   Wed, 27 Sep 2023 17:39:15 +0530
From:   David Heidelberg <david@...t.cz>
To:     Nicolas Frattaroli <frattaroli.nicolas@...il.com>,
        gregkh@...uxfoundation.org, johan@...nel.org,
        Corentin Labbe <clabbe@...libre.com>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v6 0/2] usb: serial: add support for CH348

Hello Corentin, light reminder about this patchset and Nicolas question :)

Thank you
David

On 30/08/2023 23:13, Nicolas Frattaroli wrote:
> On Mittwoch, 28. Juni 2023 15:38:32 CEST Corentin Labbe wrote:
>> Hello
>>
>> The CH348 is an octo serial to USB adapter.
>> The following patch adds a driver for supporting it.
>> Since there is no public datasheet, unfortunatly it remains some magic values.
>>
>> It was tested with a large range of baud from 1200 to 1500000 and used with
>> success in one of our kernel CI testlab.
>>
>> Regards
>>
>> [...]
> Hello,
>
> thank you for your work on this. I recently made myself a CH348
> board and used this patchset with a small test application[1]
> to see how it performs. Specifically, I ran this on an RK3566
> single board computer, connecting one serial adapter to the
> other, with the test as follows:
>
>   ./serialtest /dev/ttyUSB0 9600 # UART0 of 1st CH348 board
>   ./serialtest /dev/ttyUSB8 9600 # UART0 of 2nd CH348 board
>
> One problem I've noticed is that writes to the tty fd never
> seem to block. On two CH340 adapters I have, they do seem to
> block, whereas here, you can see from the statistics at the
> end that magnitudes more bytes were written than read, with
> seemingly most of them being discarded. From my reading of
> the termios parameters I set, this shouldn't be the case,
> right?
>
> You can see from the error percentage that it gets less
> bad as you increase the serial baudrate; I've tested up
> to 6 mbaud like this. I assume that's because less written
> bytes get discarded.
>
> Any ideas on whether I'm relying on weird driver behaviour
> with the blocking here or if this driver actually has a
> defect whereby it never signals to userspace that less
> bytes were written than have been submitted?
>
> Kind regards,
> Nicolas Frattaroli
>
> [1]: https://github.com/CounterPillow/serialtest
>
>
-- 
David Heidelberg
Certified Linux Magician