SDIO performance

[Tim Harvey]

Greetings,

Back in May of last year I was doing some evaluation of a couple of 
Marvell Libertas 88w8686 modules on an i.MX31 host running 2.6.22 using 
the libertas driver from compat-wireless.  I found at the time that the 
max throughput I could achieve was about 1.1mbps at 11M and it was 
suggested that the fact that the i.MX31's SDIO host controller driver 
did not support MMC_CAP_SDIO_IRQ and could only support 1bit transfers.  
Recently I've taken another look at the same sdio modules but this time 
running on an OMAP3 beagleboard host running 2.6.27 using the libertas 
driver from mainline.  This time I find that I can only achieve about 
0.8mbps at 11M.  

I've verified that the OMAP3's MMC/SDIO host controller driver supports 
4-bit mode yet it does not support MMC_CAP_SDIO_IRQ.  Its been suggested 
to me on #libertas that the linux core sdio driver is not very efficient 
and that also the libertas if_sdio.c support steps down to 1-bit mode 
for most transfers.  Even still 1bit SDIO has a data transfer rate of 
10MB/sec so I'm still surprised at this <1mbps performance.

Can anyone else using libertas-sdio tell me what hardware they are using 
(host and module) and what software they are using (kernel version + any 
relevant patches and libertas firmware) and what throughputs they can 
achieve?

I'm going to be digging into the if_sdio.c component and try to 
understand the linux core sdio subsystem to see if I can find any hope 
of speeding things up
 - any pointers would be greatly appreciated.

I've seen the recent patches to support GSPI devices and I wonder what 
kind of throughput has been acheived on those?

Also, as about 8mo's have passed since I looked for hardware supported 
by the libertas driver, are there any recent USB dongle devices 
supported out there?  The information on 
http://linuxwireless.org/en/users/Drivers/libertas hasn't changed in 
quite some time and I'm not sure if its up-to-date.

Thanks,

Tim