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

[Anton Bondarenko]

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/