Hi,
On 30-09-15 03:52, wens Tsai wrote:
Hi,
I've been looking into AXP223 usage as part of the RSB patches.
I found that the recommended voltage for VDD-SYS is 1.1V, but
we default to 1.2V in U-boot. Among the fex files, some use
1.1V and some use 1.2V.
Right, I happened to be looking the same thing recently.
I've recently bought a bunch of 2nd hand q8 tablets, and I've
pushed all the fex files I got from them to sunxi-boards yesterday.
Looking at A23 devices only the ippo_q8h_v1.0.fex and
ippo_q8h_v1.2.fex files set VDD-SYS to 1.2 volt, the other
7 use the recommended 1.1V value. Also note that the gt90h-v4
tablet which I have does not work with a VDD-SYS of 1.2 volt,
it only works with a VDD-SYS of 1.1 volt.
I've tested my ippo_q8h_v1.2 and it works fine with a VDD-SYS
of 1.1 volt.
Looking at A33 devices there are 2 outliers the TZX-723Qa4 and
astar_mid756.fex both set VDD-SYS to 1.26 V, rather then to 1.1 V.
The other 6 all use 1.1V so I believe that 1.1V indeed is a better
default.
Perhaps we could update the defconfigs with the values from
the fex files.
I think that we should switch the default to 1.1V and then if we see
any issues set it to 1.2V in individual defconfig-s.
One thing that we have to be careful of is matching the settings
in U-boot and the kernel, or alternatively, not use a fixed value
but the recommended range for the VDD-SYS regulator. Accidentally
dropping the voltage on VDD-SYS results in some logic errors,
which likely lead to a crash.
I think it is best to set a range in the dts file and the kernel
just inherit whatever u-boot has set up, this way we don't end
up changing vdd-sys half-way through boot, and we only have one
place where to tweak it if necessary.
Regards,
Hans
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