[U-Boot] [PATCH v2 1/4] udoo: Add ethernet support (FEC + Micrel KSZ9031).

[Giuseppe Pagano <giuseppe.pagano@seco.com>]

On Mon, 2013-11-18 at 18:05 +0100, Giuseppe Pagano wrote:
> 
> > 
> > > +	ksz9031_phy_extended_write(phydev, 0x02,
> > > +				   MII_KSZ9031_EXT_RGMII_CLOCK_SKEW,
> > > +				   MII_KSZ9031_MOD_DATA_NO_POST_INC, 0x03FF);
> > 
> I have september 2012 revision of KSZ9031's manual, and I think it is
> complete enough about skew parameter (preliminary version was not). 
> Default value for GTX_CLK and RX_CLK swek register is 0x001ef (0 ns
> delay for both). I use maximum positive delay (value 0x03ff) as safe
> value, but it doesn't work on every board.

To be more clear (for people who do not have KSZ9031 manual). 
GTX and RX skew delay have 5 bit resolution, so
MII_KSZ9031_EXT_RGMII_CLOCK_SKEW register have this default value bit:

reserved   GTX skew   RX skew
 0000_00----01_111-----0_1111   (0x01EF -> 0ns delay)
 0000_00----00_000-----0_0000   (0x0000 -> -0.96ns delay both)
 0000_00----11_111-----1_1111   (0x03FF -> +0.96ns delay both)
 0000_00----11_111-----0_1111   (0x03EF -> +0.96ns delay only for GTX)
etc.


> 
> Best regards
> Giuseppe Pagano