linux-kernel - Re: [PATCH] Revert "USB: serial: ch341: fix character loss at high transfer rates"

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Message-ID: <20210824123232.GA25435@1wt.eu>
Date:   Tue, 24 Aug 2021 14:32:32 +0200
From:   Willy Tarreau <w@....eu>
To:     Johan Hovold <johan@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paul Größel <pb.g@....de>,
        stable@...r.kernel.org
Subject: Re: [PATCH] Revert "USB: serial: ch341: fix character loss at high
 transfer rates"

On Tue, Aug 24, 2021 at 02:19:26PM +0200, Johan Hovold wrote:
> This reverts commit 3c18e9baee0ef97510dcda78c82285f52626764b.
> 
> These devices do not appear to send a zero-length packet when the
> transfer size is a multiple of the bulk-endpoint max-packet size. This
> means that incoming data may not be processed by the driver until a
> short packet is received or the receive buffer is full.
> 
> Revert back to using endpoint-sized receive buffers to avoid stalled
> reads.

Sorry for this, I didn't notice any issue here (aside for the chip
working where it used not to). I have no idea what these zero-length
packets correspond to, nor why they're affected by the transfer size.
Do you have any idea what I should look for ? Because without that
patch, the device is unusable for me :-/

Thanks!
Willy