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

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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.