Quick question on vt8237 smbus

[Corey Osgood]

I'm working on vt8237 smbus in v3, and I had a quick question, mostly for
Rudolf Marek and Bari, but feel free to jump in with your 2 cents:

u8 smbus_read_byte(u16 dimm, u8 offset, u16 smbus_io_base)
{
    u8 val;

printk(BIOS_SPEW, "SMBus Read from DIMM %1x at address 0x%4x\n",
                dimm, offset);

smbus_reset(smbus_io_base);

/* Clear host data port. */
    outb(0x00, smbus_io_base + SMBHSTDAT0);
    //SMBUS_DELAY();
    smbus_wait_until_ready(smbus_io_base);

dimm = (dimm << 1) | 1;

outb(dimm, smbus_io_base + SMBXMITADD);

The dimm = (dimm << 1) | 1 is something that came from a via southbridge
porting guide (NOT the one for the vt8237r, I don't have that one). With it,
my spd addresses are 0x50, 0x51, etc, without it, they'd be 0xa1, 0xa3, etc.
Which would be preferred? Do you think we'd ever need a 0xa0 or 0xa2
address?

Thanks,
Corey

[ron minnich]

On Mon, Oct 13, 2008 at 11:36 AM, Corey Osgood  wrote:
> I'm working on vt8237 smbus in v3, and I had a quick question, mostly for
> Rudolf Marek and Bari, but feel free to jump in with your 2 cents:
>
> u8 smbus_read_byte(u16 dimm, u8 offset, u16 smbus_io_base)
> {
>     u8 val;
> printk(BIOS_SPEW, "SMBus Read from DIMM %1x at address 0x%4x\n",
>             dimm, offset);
>
> smbus_reset(smbus_io_base);
>
> /* Clear host data port. */
> outb(0x00, smbus_io_base + SMBHSTDAT0);
> //SMBUS_DELAY();
> smbus_wait_until_ready(smbus_io_base);
>
> dimm = (dimm << 1) | 1;
>
> outb(dimm, smbus_io_base + SMBXMITADD);
>
> The dimm = (dimm << 1) | 1 is something that came from a via southbridge
> porting guide (NOT the one for the vt8237r, I don't have that one). With it,
> my spd addresses are 0x50, 0x51, etc, without it, they'd be 0xa1, 0xa3, etc.
> Which would be preferred? Do you think we'd ever need a 0xa0 or 0xa2
> address?

stick with 0x50 etc. The SMBUS address is the high 7 bits with opcode
in the lowest bit. So a1, a3, etc. are not real addresses. 50 and 51
are.

ron

[Marc Jones]

Corey Osgood wrote:
> I'm working on vt8237 smbus in v3, and I had a quick question, mostly 
> for Rudolf Marek and Bari, but feel free to jump in with your 2 cents:
> u8 smbus_read_byte(u16 dimm, u8 offset, u16 smbus_io_base)
> {
>     u8 val;
>
>     printk(BIOS_SPEW, "SMBus Read from DIMM %1x at address 0x%4x\n",
>                 dimm, offset);
>
>     smbus_reset(smbus_io_base);
>
>     /* Clear host data port. */
>     outb(0x00, smbus_io_base + SMBHSTDAT0);
>     //SMBUS_DELAY();
>     smbus_wait_until_ready(smbus_io_base);
>
>     dimm = (dimm << 1) | 1;
>
>     outb(dimm, smbus_io_base + SMBXMITADD);
>
>
> The dimm = (dimm << 1) | 1 is something that came from a via southbridge 
> porting guide (NOT the one for the vt8237r, I don't have that one). With 
> it, my spd addresses are 0x50, 0x51, etc, without it, they'd be 0xa1, 
> 0xa3, etc. Which would be preferred? Do you think we'd ever need a 0xa0 
> or 0xa2 address?

My 2cents.
I have never really cared for the <<1. I prefer the more normal IO 
address. Most platform specs I have seen indicate the spd device at 
0xA0, 0xA2, etc.

Marc

[Rudolf Marek]

Hi,

0x50 is the actual address. 0xA0 is actual encoded address which starts from 
bit1. bit0 indicates if it is R/W operation.

I would prefer to stick with 0x50.

Rudolf

[Peter Stuge]

Corey Osgood wrote:
> u8 smbus_read_byte(u16 dimm, u8 offset, u16 smbus_io_base)

..
> dimm = (dimm << 1) | 1;

..
> With it, my spd addresses are 0x50, 0x51, etc, without it, they'd
> be 0xa1, 0xa3, etc. Which would be preferred?

As others have said, the input to this function should be 0x50.
> Do you think we'd ever need a 0xa0 or 0xa2 address?

The bus just has 7 bits for address so no problem.

//Peter

[Corey Osgood]

On Mon, Oct 13, 2008 at 3:26 PM, Peter Stuge  wrote:
> Corey Osgood wrote:
> > u8 smbus_read_byte(u16 dimm, u8 offset, u16 smbus_io_base)
>
> ..
> > dimm = (dimm << 1) | 1;
>
> ..
> > With it, my spd addresses are 0x50, 0x51, etc, without it, they'd
> > be 0xa1, 0xa3, etc. Which would be preferred?
>
> As others have said, the input to this function should be 0x50.

Alright, that was what I was thinking too. Thanks for the quick responses!

-Corey