[U-Boot] [PATCH v2] spi: omap3: Fix timeout handling

[Tom Rini]

On Wed, Apr 01, 2015 at 04:21:50PM +0100, Andy Pont wrote:
> Hi David,
> 
> <snipped for brevity>
> 
> >  	for (i = 0; i < len; i++) {
> >  		/* wait till TX register is empty (TXS == 1) */
> > +		start = get_timer(0);
> >  		while (!(readl(&ds->regs->channel[ds->slave.cs].chstat) &
> >  			 OMAP3_MCSPI_CHSTAT_TXS)) {
> > -			if (--timeout <= 0) {
> > +			if (get_timer(start) > SPI_WAIT_TIMEOUT) {
> >  				printf("SPI TXS timed out, status=0x%08x\n",
> >  				       readl(&ds->regs->channel[ds-
> > >slave.cs].chstat));
> >  				return -1;
> 
> I have a couple of questions...
> 
> Firstly, when in SPL is there access to the get_timer() function?

We call timer_init() from board_init_r() in SPL, prior to diving down
into loading (or checking for Falcon vs Regular) so this is safe.

> Secondly, when using Falcon mode to load Linux directly from SPI (Falcon
> mode) then we want to maximise the throughput and save every CPU cycle we
> possibly can.  Adding yet another function call into the for loop and hence
> calling it a couple of million times seems, on the face of it, like it is
> going to slow things down.

I'd like to see measurements to prove me wrong but this both seems like
a bad idea (optimizing by being incorrect, this gives us a correct
timeout check like other drivers do) and really unlikely I would think
to be noticable.  Since we'll be doing the same code-paths in both
regular and SPL, trying to time things (by loading a big file) would be
easy enough I think.  Thanks!

-- 
Tom
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