i2c/kernel i2c-algo-bit.c

[khali@linux-fr.org (Jean Delvare)]

> Modified Files:
> 	i2c-algo-bit.c 
> Log Message:
> (Khali) Fix sclhi() for adapters that do not have getscl().
>         Enable bit_test for adapters that do not have getscl().
>         Mostly rewrite test_bus(), cleaner and probably faster.

I'd like reviewers and testers on this, since I plan to submit a similar
for Linux 2.6. There are two distinct changes:

1* Fixed sclhi() for adapters that do not have getscl(). It looks like
there was a udelay call missing in this case.

2* Rewrote test_bus() almost entirely, to allow adapters without
getscl() to be tested. It's still interesting to test SDA in this case.

I have a pair of questions with regard to i2c-algo-bit:

1* I don't understand how the whole thing works. Each of sdalo(),
sdahi(), scllo() and sclhi() are waiting adap->udelay before returning.
How in this condition can the driver change both SCL and SDA values in a
row?

2* It looks like i2c-algo-bit assumes that both SDA and SCL are high by
the time it is called. Why that? Looks like not all drivers will do so.
Especially, I tried my changes using i2c-matroxfb and it looks like this
driver doesn't set SDA not SCL before registering with i2c-algo-bit,
causing bit_test to sometimes fail with the message "seems to be busy".
I wonder if it wouldn't be easier (and safer) not to assume anything
about SDA and SCL in i2c-algo-bit.c:test_bus() (that is, remove that
"may be busy" test).

-- 
Jean Delvare
http://www.ensicaen.ismra.fr/~delvare/