linux-kernel - Re: [PATCH] tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done

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Date:   Wed, 11 Jan 2017 08:09:09 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Richard Genoud <richard.genoud@...il.com>
Cc:     Gil Weber <webergil@...il.com>,
        Nicolas Ferre <nicolas.ferre@...el.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "#4 . 4+" <stable@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Subject: Re: [PATCH] tty/serial: atmel: RS485 half duplex w/DMA: enable RX
 after TX is done

On Mon, Jan 02, 2017 at 03:14:37PM +0100, Richard Genoud wrote:
> 2017-01-02 12:53 GMT+01:00 Alexandre Belloni
> <alexandre.belloni@...e-electrons.com>:
> > On 06/12/2016 at 13:05:33 +0100, Richard Genoud wrote :
> >> When using RS485 in half duplex, RX should be enabled when TX is
> >> finished, and stopped when TX starts.
> >>
> >> Before commit 0058f0871efe7b01c6 ("tty/serial: atmel: fix RS485 half
> >> duplex with DMA"), RX was not disabled in atmel_start_tx() if the DMA
> >> was used. So, collisions could happened.
> >>
> >> But disabling RX in atmel_start_tx() uncovered another bug:
> >> RX was enabled again in the wrong place (in atmel_tx_dma) instead of
> >> being enabled when TX is finished (in atmel_complete_tx_dma), so the
> >> transmission simply stopped.
> >>
> >> This bug was not triggered before commit 0058f0871efe7b01c6
> >> ("tty/serial: atmel: fix RS485 half duplex with DMA") because RX was
> >> never disabled before.
> >>
> >> Moving atmel_start_rx() in atmel_complete_tx_dma() corrects the problem.
> >>
> >> Cc: stable@...r.kernel.org
> >> Reported-by: Gil Weber <webergil@...il.com>
> >> Tested-by: Gil Weber <webergil@...il.com>
> >> Signed-off-by: Richard Genoud <richard.genoud@...il.com>
> >
> > Acked-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> >
> Greg, could you take this patch in your tree ?

Yes, will do so, thanks.

greg k-h