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powerpc/t4240qds: Add VDD override

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Allow VDD voltage overriding with a command. This is an add-on feasture of
VID. To override VDD, use command vdd_override with the value of voltage
in mV, for example

vdd_override <voltage in mV, eg. 1050>

The above example will set the VDD to 1.050 volt. Any wrong value out of
range of 0.8188 to 1.2125 volt or invalid string is ignored.

In addition to the command, if overriding VDD is needed earlier in booting
process, save an variable and reboot:

setenv t4240qds_vdd_mv <voltage in mV>
saveenv

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
This commit is contained in:
York Sun
2013-03-25 07:40:01 +00:00
committed by Andy Fleming
parent 0c9ab437de
commit 0aadf4aa51
2 changed files with 61 additions and 2 deletions
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24
doc/README.t4240qds
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@@ -96,3 +96,27 @@ The addresses in brackets are physical addresses.
0x0_ffff_f000 (0x0_7fff_fff0) - 0x0_ffff_ffff 4KB Boot page translation for secondary cores
The physical address of the last (boot page translation) varies with the actual DDR size.
Voltage ID and VDD override
--------------------
T4240 has a VID feature. U-boot reads the VID efuses and adjust the voltage
accordingly. The voltage can also be override by command vdd_override. The
syntax is
vdd_override <voltage in mV>, eg. 1050 is for 1.050v.
Upon success, the actual voltage will be read back. The value is checked
for safety and any invalid value will not adjust the voltage.
Another way to override VDD is to use environmental variable, in case of using
command is too late for some debugging. The syntax is
setenv t4240qds_vdd_mv <voltage in mV>
saveenv
reset
The override voltage takes effect when booting.
Note: voltage adjustment needs to be done step by step. Changing voltage too
rapidly may cause current surge. The voltage stepping is done by software.
Users can set the final voltage directly.