Re: [PATCH v4 01/16] spi: dw: Add Tx/Rx finish wait methods to the MID DMA

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Fri, May 22, 2020 at 01:18:20PM +0100, Mark Brown wrote:
> On Fri, May 22, 2020 at 03:12:21PM +0300, Andy Shevchenko wrote:
> > On Fri, May 22, 2020 at 02:52:35PM +0300, Serge Semin wrote:
> 
> > > Please, see it's implementation. It does atomic delay when the delay value
> > > is less than 10us. But selectively gets to the usleep_range() if value is
> > > greater than that.
> 
> > Oh, than it means we may do a very long busy loop here which is not good at
> > all. If we have 10Hz clock, it might take seconds of doing nothing!
> 
> Realistically it seems unlikely that the clock will be even as slow as
> double digit kHz though, and if we do I'd not be surprised to see other
> problems kicking in.  It's definitely good to handle such things if we
> can but so long as everything is OK for realistic use cases I'm not sure
> it should be a blocker.

Perhaps some kind of warning? Funny that using spi_delay_exec() will issue such
a warning as a side effect of its implementation.

-- 
With Best Regards,
Andy Shevchenko