linux-kernel - Re: [PATCH] tty: serial: qcom_geni_serial: Fix wrap around of TX buffer

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Date:   Wed, 19 Dec 2018 10:49:26 -0800
From:   Evan Green <evgreen@...omium.org>
To:     mka@...omium.org
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        msavaliy@...eaurora.org, ryandcase@...omium.org,
        Doug Anderson <dianders@...omium.org>
Subject: Re: [PATCH] tty: serial: qcom_geni_serial: Fix wrap around of TX buffer

On Wed, Dec 19, 2018 at 10:17 AM Matthias Kaehlcke <mka@...omium.org> wrote:
>
> Before commit a1fee899e5bed ("tty: serial: qcom_geni_serial: Fix
> softlock") the size of TX transfers was limited to the TX FIFO size,
> and wrap arounds of the UART circular buffer were split into two
> transfers. With the commit wrap around are allowed within a transfer.
> The TX FIFO of the geni serial port uses a word size of 4 bytes. In
> case of a circular buffer wrap within a transfer the driver currently
> may write an incomplete word to the FIFO, with some bytes containing
> data from the circular buffer and others being zero. Since the
> transfer isn't completed yet the zero bytes are sent as if they were
> actual data.
>
> Handle wrap arounds of the TX buffer properly and ensure that words
> written to the TX FIFO always contain valid data (unless the transfer
> is completed).
>
> Fixes: a1fee899e5bed ("tty: serial: qcom_geni_serial: Fix softlock")
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>

Oh nice, so this did end up being your problem with corrupt
characters? Strange though, I still would have expected this bug to
result in inserted serial characters, rather than edited ones.
Either way, this looks good to me.

Reviewed-by: Evan Green <evgreen@...omium.org>