linux-kernel - Re: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated one

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Date:	Sat, 14 Nov 2015 11:01:53 +0100
From:	Anton Bondarenko <anton.bondarenko.sama@...il.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	broonie@...nel.org, b38343@...escale.com,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	vladimir_zapolskiy@...tor.com, jiada_wang@...tor.com
Subject: Re: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated
 one


On 11.11.2015 09:12, Sascha Hauer wrote:
> On Tue, Nov 10, 2015 at 09:20:06PM +0100, Anton Bondarenko wrote:
>>
>>
>> On 05.11.2015 09:47, Sascha Hauer wrote:
>>>> @@ -890,12 +891,40 @@ static void spi_imx_dma_tx_callback(void *cookie)
>>>>   	complete(&spi_imx->dma_tx_completion);
>>>>   }
>>>>
>>>> +static int spi_imx_calculate_timeout(struct spi_imx_data *spi_imx, int size)
>>>> +{
>>>> +	unsigned long coef1 = 1;
>>>> +	unsigned long coef2 = MSEC_PER_SEC;
>>>> +	unsigned long timeout = 0;
>>>> +
>>>> +	/* Swap coeficients to avoid div by 0 */
>>>> +	if (spi_imx->spi_bus_clk < MSEC_PER_SEC) {
>>>> +		coef1 = MSEC_PER_SEC;
>>>> +		coef2 = 1;
>>>> +	}
>>>> +
>>>> +	/* Time with actual data transfer */
>>>> +	timeout += DIV_ROUND_UP(8 * size * coef1,
>>>> +				spi_imx->spi_bus_clk / coef2);
>>>> +
>>>> +	/* Take CS change delay related to HW */
>>>> +	timeout += DIV_ROUND_UP((size - 1) * 4 * coef1,
>>>> +				spi_imx->spi_bus_clk / coef2);
>>>> +
>>>> +	/* Add extra second for scheduler related activities */
>>>> +	timeout += MSEC_PER_SEC;
>>>> +
>>>> +	/* Double calculated timeout */
>>>> +	return msecs_to_jiffies(2 * timeout);
>>>> +}
>>>
>>> I think you can simplify this function to:
>>>
>>> 	timeout = size * 8 / spi_imx->spi_bus_clk;
>>> 	timeout += 2;
>>>
>>> 	return msecs_to_jiffies(timeout * MSEC_PER_SEC);
>>>
>>> The rationale is that when size * 8 / spi_imx->spi_bus_clk is 0 then we
>>> can add another second and be fine. No need to calculate this more
>>> accurate, in the end it's important to catch the timeout. If we do this
>>> one or two seconds too late doesn't matter.
>>>
>>> Sascha
>>>
>>
>> Sascha,
>>
>> What about something like this:
>> 	timeout = size * (8 + 4) / spi_imx->spi_bus_clk;
>> 	timeout += 2;
>>
>> 	return msecs_to_jiffies(2 * timeout * MSEC_PER_SEC);
>>
>> I think we still need to take into account 4 CLKs between each burst.
>
> Fine with me.
>
> Sascha
>
>

Tested new implementation successfully. Will be V4 patchset. Does anyone 
has other comments regarding this commit?

Regards, Anton
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