[PATCH] spi: atmel: Prevent false timeouts on long transfers

[Mark Brown]

On Fri, Jun 16, 2023 at 06:15:35PM +0200, Miquel Raynal wrote:
> broonie at kernel.org wrote on Fri, 16 Jun 2023 15:20:27 +0100:

> > On Fri, Jun 16, 2023 at 04:12:25PM +0200, Miquel Raynal wrote:

> > > -#define SPI_DMA_TIMEOUT		(msecs_to_jiffies(1000))
> > > +#define SPI_DMA_MIN_TIMEOUT	(msecs_to_jiffies(1000))
> > > +#define SPI_DMA_TIMEOUT_PER_10K	(msecs_to_jiffies(4))  

> > Given that we know the bus speed can't we just calculate this like other
> > drivers do (we should probably add a helper TBH)?

> I agree we should probably have some kind of easy-to-use helper to
> derive a decent timeout value. How do sound the heuristics
> proposed here to you ? That would be:

> 	timeout = 1s + 4ms/10k

Like I say we should know the transfer speed so we can do better than
4ms/10k - we know how long it takes to clock out each byte, we can just
multiply that by the size of the transfer then add some fudge factor for
setup/teardown overhead.  1s feels pretty generous too.  The sun6i
driver for example does 

   max(tfr->len * 8 * 2 / (tfr->speed_hz / 1000), 100U)

and just doubles the length based timeout with a minimum of 100ms which
seems reasonable.
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