[Openchrome-users] DVI-02 funkiness

[Philip Prindeville]

Thomas Hellstr?m wrote:
> Philip Prindeville wrote:
>
>   
>> Well, I'm going through my Xorg.0.log on my SP-13000, and
>> seeing in it:
>>
>> (II) VIA(0): ViaI2CBus3Init
>> (II) VIA(0): I2C bus "I2C bus 3" initialized.
>> (II) VIA(0): ViaI2CScan: Scanning I2C bus 2
>> (II) VIA(0): ViaI2CScan: Scanning I2C bus 3
>> (--) VIA(0): Found slave on I2C bus 3 - 0x40
>> (--) VIA(0): Found slave on I2C bus 3 - 0x70
>> (--) VIA(0): Found slave on I2C bus 3 - 0x74
>> (--) VIA(0): Found slave on I2C bus 3 - 0xA0
>>
>>
>> so I hacked up a driver to try to read a byte from Bus 3, address 0x70,
>> sub-address 0x00: which should be the first byte of the Sil164 device...
>> but the read fails.
>>
>> So...  why is the read failing?  Is the bus not being
>> initialized with the correct timings?
>>
>> Or are there things that don't have stuff starting at sub-address 0?
>>
>> Also, going through the Via drivers to try to figure how they do
>> things...  I notice that they also probe using something called
>> GPIOI2C_*
>>
>> Not sure what that is.  Is there another I2C bus that isn't
>> accessible with the xf86i2c.c code?  Has anyone else pored over
>> that part of the VT code?
>>
>> Thanks,
>>
>> -Philip
>>
>>
>>  
>>
>>     
> Luc once moved VIA's GPIOI2C_ stuff over to the generic xf86i2c code.
> IIRC, While doing so, he altered some timings in order to make it work 
> with a chip he had on his mainboard. Those alterations made it fail 
> reading from the vt1623 device, it even got the device id wrong, so I 
> changed those timings back to something like what's in the VIA code to 
> make vt1623 working.
>
> It's possible that the read timing needs more tweaking. Try to compare 
> the failing function with the corresponding one in the VIA code and see 
> if you can make it work
>
> /Thomas
>   


That's the thing: the Via code defaults the xf86I2CBusRec
initialization... and the driver also clones the DevRec values
from the bus they are attached to.

But looking at the actual read/write routines that they plug
in as handlers, there are no delays at all!

static void
VIAI2C1GetBits(I2CBusPtr b, int *clock, int *data)
{
    CARD8 reg;

    outb(0x3c4, 0x26);
    reg = inb(0x3c5);

    *clock = (reg & DDC_SCL_READ_MASK) != 0;
    *data  = (reg & DDC_SDA_READ_MASK) != 0;
}



The code just runs "flat out", no delays.

I'm thinking that maybe the BusRec should
be initialized with no delays, but that the VT1623
driver should have locally-specified delays.

-Philip