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p4080ds: add README.p4080ds which documents the "serdes" hwconfig option 

Add documentation for the "serdes" hwconfig option, which is used to
specify the status of SerDes banks two and three for the SERDES8 erratum
work-around.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
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Timur Tabi 2011-03-25 14:11:48 -05:00 committed by Kumar Gala
parent 15321c9c39
commit 6c7a29a5b4
1 changed files with 32 additions and 0 deletions
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Overview
--------
The P4080DS is a Freescale reference board that hosts the eight-core P4080 SOC.
SerDes hwconfig configuration
-----------------------------
The P4080 RCW includes three sets of bits the specify which SerDes lanes
should be powered down: SRDS_LPD_B1 (for bank one), SRDS_LPD_B2 (for bank two),
and SRDS_LPD_B3 (for bank three). Each of these contains four bits, one for
each lane in the bank. SerDes Erratum SERDES8 requires that SRDS_LPD_B2 and
SRDS_LPD_B3 be set to 0b1111. This forces banks two and three to be powered
down at reset.
To re-enable these banks in U-Boot, two hwconfig are available:
"fsl_srds_lpd_b2" and "fsl_srds_lpd_b3". The value passed via fsl_srds_lpd_b2
is written into SRDS_LPD_B2, and the value passed via fsl_srds_lpd_b3 is into
SRDS_LPD_B3. Each bit represents one of each bank, and a value of '1'
indicates that the lane should be powered down.
For example, to indicate that both SerDes banks 2 and 3 are powered down, add
the following to hwconfig:
serdes:fsl_srds_lpd_b2=0xf,fsl_srds_lpd_b3=0xf
The "0xf" is a mask that corresponds to the 4 lanes A-D. The most significant
bit corresponds to lane A. To indicate that just lane A of bank 3 is to be
powered down, use:
serdes:fsl_srds_lpd_b3=8
These options should be specified only if U-Boot does not automatically power
on the correct lanes.