GSPI and SDIO performance for 8686

[Dan Williams]

On Wed, 2009-07-29 at 09:59 -0700, Tim Harvey wrote:
> Greetings,
> 
> I've seen a lot of activity lately and development of the GSPI interface 
> for libertas.  What max throughput have people been able to get with an 
> 8686 talking over GSPI?
> 
> My previous evaluation with an 8686 talking over SDIO (both to an i.MX31 
> SDHC on a patched 2.6.22 and to an OMAP3x SDHC on 2.6.28 beagleboard) 
> showed a horribly slow max throughput of about 1.4mbps.  Has anyone seen 
> better performance in recent libertas/kernel with the OMAP3x SDHC (ie 
> talking to the 8686 on an Overo Fire/Air)?

Any horrible SDIO performance you've seen has got to be dependent on
either HZ or the SDHC.  I've routinely pulled 11 or 12 Mbps with normal
laptop Ricoh R5C822 controllers.  Now maybe there's scheduling latency
or something in the libertas code that erroneously ratelimits related to
HZ, but we know we can pull respectable rates out of the card if the
SDHC doesn't suck.  So we've got a baseline.  At this point, I suspect
the host controller and platform code more than I suspect the libertas
driver or the 8686 chip/firmware given this baseline.

Dan