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

[Anton Bondarenko]

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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