Subject: [PATCH 1/3] serial: mxs-auart: implement flush_buffer hook

From: [email-masked] (Hector Palacios)
Date: Fri, 29 Nov 2013 18:49:42 +0100

Hi Marek,

On 11/29/2013 05:50 PM, Marek Vasut wrote:
> Hello Hector,
>
>> Terminate any DMA transfer and verify the TX FIFO is empty.
>>
>> Signed-off-by: Hector Palacios <[email-masked]>
>> ---
>>   drivers/tty/serial/mxs-auart.c | 23 +++++++++++++++++++++++
>>   1 file changed, 23 insertions(+)
>>
>> diff --git a/drivers/tty/serial/mxs-auart.c
>> b/drivers/tty/serial/mxs-auart.c index 9f0461778fc1..d9bf6e103f65 100644
>> --- a/drivers/tty/serial/mxs-auart.c
>> +++ b/drivers/tty/serial/mxs-auart.c
>> @@ -782,6 +782,28 @@ static unsigned int mxs_auart_tx_empty(struct
>> uart_port *u) return 0;
>>   }
>>
>> +/*
>> + * Flush the transmit buffer.
>> + * Locking: called with port lock held and IRQs disabled.
>> + */
>> +static void mxs_auart_flush_buffer(struct uart_port *u)
>> +{
>> +	struct mxs_auart_port *s = to_auart_port(u);
>> +	struct dma_chan *channel = s->tx_dma_chan;
>> +	unsigned int to;
>> +
>> +	if (auart_dma_enabled(s)) {
>> +		/* Avoid deadlock with the DMA engine callback */
>> +		spin_unlock(&s->port.lock);
>> +		dmaengine_terminate_all(channel);
>> +		spin_lock(&s->port.lock);
>
> Can you not maybe just set some flag here to tell the DMA engine callback things
> are shutting down and to don't do anything funny anymore ?

I copied these spin_lock protections from the amba-pl011.c driver.
The callbacks in the mxs-auart driver are not taking the lock but I was not sure if 
any of the serial core functions they call are, so I thought it was a good idea to 
take it.

>> +	}
>> +	/* Wait for the FIFO to flush */
>> +	to = u->timeout;
>> +	while (!mxs_auart_tx_empty(u) && to--)
>> +		mdelay(1);
>
> Maybe you can put some cond_resched() into the loop to avoid wasting too many
> cycles ?

Do you mean like this? Ok

	while (!mxs_auart_tx_empty(u) && to--) {
		cond_resched();
		mdelay(1);
	}

Best regards,
--
Hector Palacios