[i2c] i2c-i801: Regression between 2.6.22.9 & 2.6.23.9

[Jean Delvare]

On Wed, 09 Jan 2008 14:47:20 +0100, Ivo Manca wrote:
> Jean Delvare wrote:
> > What is an "EEP OM"?
>
> Sorry, that should read "EEPROM" ofcourse.

Err, of course. I'm not very smart today it seems...

> > Please note that EEPROMs typically want I2C block reads (mode "i" of
> > i2cdump) and not SMBus block reads. Using the wrong mode shouldn't hang
> > the bus though.
>
> I know; however, i2cdump states my bus doesn't have i2c block read
> capabilities. That's why I used SMBus block reads, which seemed to work
> properly.

OK. This is an important fact when tracking this regression. I guess
that the 1st byte returned by your EEPROM is 0x80, which is NOT a valid
SMBus block length. This means that it is expected that an error is
returned. It wasn't the case before (the invalid length was adjust to
the nearest valid valid length, i.e. 32) but that was changed in 2.6.23
to return an error instead, and I think this is the right thing to do:

>                 if (i == 1 && read_write == I2C_SMBUS_READ) {
>                         len = inb_p(SMBHSTDAT0);
> -                       if (len < 1)
> -                               len = 1;
> -                       if (len > 32)
> -                               len = 32;
> +                       if (len < 1 || len > I2C_SMBUS_BLOCK_MAX) {
> +                               result = -1;
> +                               goto END;
> +                       }
>                         data->block[0] = len;
>                 }

So, the fact that you get an error with 2.6.23 when you did not in
2.6.22 is expected, this is not a regression. I get the same error on
my test system. The only difference is that it does NOT hang the bus
for me.

BTW, I2C block read is now supported in -mm:
http://khali.linux-fr.org/devel/linux-2.6/jdelvare-i2c/i2c-i801-04-add-support-for-i2c-block-read.patch

Note that the chip you have at 0x69 is most certainly a clock chip and
many clock chip do support the SMBus block read transaction. This is
how I test it, maybe you can try this and see if it hangs as well or
not.

> Since I was using an ICH5/ICH5R, which is not listed in the switch
> statement at the probe function, I should be defaulting to isich = 0 and
> therefor using  i801_block_transaction_byte_by_byte. I'll look into the
> exact changes made here.

The ICH5 _is_ listed in the switch statement:
> 	case PCI_DEVICE_ID_INTEL_82801EB_3:

So it should use i801_block_transaction_by_block(). You might want to
test removing this case from the switch statement to force the driver
to use i801_block_transaction_byte_by_byte() instead, and see if it
makes a difference.

> > On my side I'll check if I can reproduce the problem on one of my test
> > systems. I don't test SMBus block reads very often so I could have
> > missed it.

I did that, with an ICH5 as well, I get the error when using an SMBus
block read on an EEPROM, as expected, but the bus never hangs. I have
no idea why it hangs for you and not for me. If you figure it out,
please let me know.

-- 
Jean Delvare