Re: Performance of spi_mpc83xx.c sucks.

[Peter Korsgaard <jacmet-OfajU3CKLf1/SzgSGea1oA@public.gmane.org>]

>>>>> "Joakim" == Joakim Tjernlund <joakim.tjernlund-SNLAxHN9vbcOP4wsBPIw7w@public.gmane.org> writes:

 Joakim> We have noticed that the spi_mpc83xx.c driver is very slow, the gap
 Joakim> between words are huge.
 Joakim> So I started to optimise it and it still sucks.
 Joakim> However, if I poll the SPIE_NF SPIE_NE bits instead it works MUCH
 Joakim> better, like so:

Yes, I've noticed the same. I get around ~5 times higher throughput
with a simple polled loop in U-Boot compared to under Linux (66MHz
clock).

I've written it of as simply being a question of interrupt overhead
(at 66MHz / 32bits we're talking over 2 million interrupts per
second - E.G. only ~100 instructions between each!)

Maybe it indeed makes more sense to use polling for high bitrates.

-- 
Bye, Peter Korsgaard

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