GTA series power design

[Andy Green]

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Somebody in the thread at some point said:

| *What PMU we should use for 6400/6410

The Samsung one has some nice features like codec and audio amp on board.

| *What the bus will be used for devices, we have following device for
| GTA04 for sure
|
| **WLAN (SDIO/SPI?)

If we use the same Atheros module, we should keep the driver all the
same to save trouble.  So SDIO.

| **Accelerometer (SPI)

It can help if they have an SPI bus each and don't share.

| **Debug (UART/Others?)

Private USB / FTDI --> Jtag and USB console from UART.

| **lots LED
| **Some mechanical button, some other types
| **Wolfson I2S
| **PMU I2C

I think maybe the MPU can take care of these.  If the MPU can take care
of all input device like touchscreen, motion sensors, buttons, LEDs; and
PMU and audio routing it will have advantages.

Also the communication to the MPU from CPU would likely be SPI.


| *Any bus design in hardware we could do for better power management design
|
| *Any power management project existing in open source project that could
| suit for device power management?

The new Regulator stuff

http://www.gossamer-threads.com/lists/linux/kernel/880290#880290

is designed for it.  But maybe we need to go beyond this for the simple
reason the CPU itself should be subject to these power states and not
the only way to control it.  Just like we keep the backlight turned off
as much as possible for power we need to do the same for the CPU I
think.  It really means the CPU is another peripheral on the board for
the MPU point of view it can power or suspend as it chooses.

If we assume that we have the always-on MPU connected to the PMU, then
it is the boss of the board and not the CPU.  It decides about changing
CPU power state in cooperation with Linux or not.

And I wonder how much we have to take care of in the MPU before we can
imagine to suspend the CPU entirely during a call, increasing the
battery performance for call time.


If Linux makes requests to the MPU using a simple API, we can hide
details like which PMU is used because we get a manifest from the MPU
(this device has touchscreen, backlight, WLAN power, etc) and scan ask
for "Backlight off"... how that is done Linux doesn't have to care even
if on another variant we changed PMU.

- -Andy
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