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

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Message-ID: <20170102115326.mfly6w5k3dllfpur@piout.net>
Date:   Mon, 2 Jan 2017 12:53:26 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Richard Genoud <richard.genoud@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Gil Weber <webergil@...il.com>,
        Nicolas Ferre <nicolas.ferre@...el.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] tty/serial: atmel: RS485 half duplex w/DMA: enable RX
 after TX is done

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>


-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com