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SubjectRe: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated one
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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.

Regards, Anton


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