From: hector.palacios@digi•com (Hector Palacios)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] serial: mxs-auart: wait for DMA buffer to flush before shutdown
Date: Wed, 2 Oct 2013 10:46:28 +0200 [thread overview]
Message-ID: <524BDD64.70309@digi.com> (raw)
In-Reply-To: <20131002083014.GN2548@pengutronix.de>
Hi Uwe,
On 10/02/2013 10:30 AM, Uwe Kleine-K?nig wrote:
> Hello Hector,
>
> On Wed, Oct 02, 2013 at 10:09:10AM +0200, Hector Palacios wrote:
>> On 10/02/2013 09:44 AM, Uwe Kleine-K?nig wrote:
>>> On Wed, Oct 02, 2013 at 09:31:16AM +0200, Hector Palacios wrote:
>>>> On 10/01/2013 09:48 PM, Uwe Kleine-K?nig wrote:
>>>>> On Tue, Oct 01, 2013 at 06:18:35PM +0200, Hector Palacios wrote:
>>>>>> + /* Wait enough time to flush DMA buffer completely */
>>>>>> + to = u->timeout * UART_XMIT_SIZE / u->fifosize;
>>>>> u->timeout is the time needed to send one char, right? UART_XMIT_SIZE is
>>>>> the size of the circular buffer, fifosize is the size of the fifo. I
>>>>> don't get what you get by dividing by the fifosize. I would have
>>>>> expected something like:
>>>>>
>>>>> u->timeout * min(UART_XMIT_SIZE, u->fifosize)
>>>>>
>>>>> Can you explain, maybe in a comment along the code for the next person
>>>>> not understanding?
>>>>
>>>> u->timeout is *not* the time needed to send one char but the time
>>>> needed to flush the complete port fifo (see uart_update_timeout() in
>>>> serial_core.c where it is set).
>>> Ah, right. (BTW, uart_update_timeout should better round up instead of
>>> round down, i.e.
>>> - port->timeout = (HZ * bits) / baud + HZ/50;
>>> + port->timeout = DIV_ROUND_UP(HZ * bits, baud) + HZ/50;
>>> )
>>>
>>>> UART_XMIT_SIZE is the number of bytes in the DMA buffer, so I divide
>>>> the max number of bytes in the FIFO by the FIFO size and multiply by
>>>> the FIFO timeout.
>>> ditto here, better round up. Although I think using a completion could
>>> shorten the timeout considerably because there are often less than
>>> UART_XMIT_SIZE chars in the buffer?!
>>
>> I'm not really waiting the full timeout. I'm checking for TX fifo
>> empty every 1ms and for a maximum of 'to' ms.
> Correct. Still using DIV_ROUND_UP would be better, right?
I think it is not really needed, after all the code is adding HZ/50 of slop which acts
like a round up, doesn't it?
/*
* Figure the timeout to send the above number of bits.
* Add .02 seconds of slop
*/
port->timeout = (HZ * bits) / baud + HZ/50;
Best regards,
--
Hector Palacios
next prev parent reply other threads:[~2013-10-02 8:46 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1380644315-31581-1-git-send-email-hector.palacios@digi.com>
[not found] ` <20131001194800.GL2548@pengutronix.de>
[not found] ` <524BCBC4.5050708@digi.com>
2013-10-02 7:44 ` [PATCH] serial: mxs-auart: wait for DMA buffer to flush before shutdown Uwe Kleine-König
2013-10-02 8:09 ` Hector Palacios
2013-10-02 8:30 ` Uwe Kleine-König
2013-10-02 8:46 ` Hector Palacios [this message]
2013-10-02 9:59 ` Uwe Kleine-König
[not found] ` <20131002083608.GO2548@pengutronix.de>
2013-10-02 8:53 ` Hector Palacios
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