Getting ARM/WM8350 audio and power management working in linux

Question

I have a rooted Sony prs900, running a linux 2.6.23 #2 PREEMPT kernel, for ARMv6. (Montavista linux kernel). I'm having problems with figuring out how power management works, both for running the system and for powering up and down the audio port. I can neither figure out how to read the battery/powerline status information, nor get the audio chip to play sound, etc ... although I have been studying the kernel modules for a while...

It's worth a little money for help, say $100 paypal donation to an email account, (or more if this takes a long time...) for the first person able to explain to me how to do them in a way that works. Eg: read battery status, and change some power modes like getting the audio amplifiers to power up/down so that the audio played to /dev/dsp (oss emulation) actually comes out as sound rather than just being consumed by the chip and ignored...

The actual sony kernel, and binary packages of cross compiler tools are located on the main page. Actual kernel sourcecode is also available.

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What I have learned so far myself :

The sony is using a wolfson micro WM8350 audio driver and battery charger/power management chip for all the system's power; eg: it can power down/up the SD memory cards, send more power to the cpu, power up audio amplifiers, etc. See: WM8350 Datasheet.

Pretty much, the whole problem revolves around getting the WM8350 kernel drivers to work... Although the company brags quite a bit about it's support under linux, they don't have any application notes or examples that are actually helpful that I can find, other than the datasheet. I suspect the kernel drivers I have are beta code, because they don't seem to be behaving well (several error messages in the kernel log about wm8350 registers not being readable happen at every boot even when running only the sony's native software...).

The kernel driver's source-code of most interest are in: linux-2.6.23_091126/drivers/mxc/pmic/{core,wm8350} Notice, the wm8350 is a competitor to the MC14783, but the linux kernel drivers use the same {core} driver source code for both chips; The sony ONLY has the wm8350 on it -- there is no MC14783 present.

The code that I most want most desperately to understand how to make operate is found in the subdirectory {wm8350}, eg: wm8350/wm8350pm/power_supply_sysfs.c.

I want the audio to fire up too, but 'm not quite sure where the pertinent audio amplifier code is yet...

Very clearly the wm8350pm code is designed to export a /sys directory interface; right now /sys is mounted and operational on the system; but I'm not very familiar with the semantics of these newer style interfaces... they aren't quite like the old APM power interfaces for Linux laptops...

First I checked the obvious: If I do a "cat /sys/power/state" it returns the word "mem" and nothing else. The file has permissions -rw-r--r--, so potentially it could be written -- but I don't know with what. The string "mem" does not exist anywhere in the source code for the wm8350pm drivers, so I don't even know if /sys/power/state is part of the source code.

Doing a find /sys -iname "wm8350" reveals a handful of directories with the patterns: wm8350-rtc , wm8350-pmic , wm8350-bl , wm8350-power , wm8350-led wm8350-hifi-dai , wm8350-codec wm8350-imx32ads.0

So, I do an ls-l on each directory, and look for actual files rather than symbolic links or subdirectories, and what I find are stock useless writable files: bind, unbind, uevent,

and a very few read only files: pmic_reg, dapm_widget, modalias, codec_reg which aren't very helpful.

It's no surprise that:

Doing: cat /sys/devices/platform/wm8350-ebx5016-audi/modalias gives "wm8350-ebx5016-audio"

Doing: cat /sys/devices/platform/wm8350-imx32ads.0/modalias gives "wm8350-imx32ads"

and since audio is off... Doing: cat /sys/devices/platform/wm8350-ebx5016-audi/dapm_widget reveals the audio state:

Headphone Jack: Off
Line In Jack: On
Mic Bias: Off
Left DAC: Off
Right DAC: Off
... (all else off and omitted except )...
EBX5016-hifi: PM State: D3hot

The last two files, I expect should do wm8350 chip register dumps... and one did. Doing: cat /sys/devices/wm8350-pmic/pmic-reg causes a long pause, then nothing is printed. but: Doing: cat /sys/devices/wm8350/platform/wm8350-ebx5016-audi/wm8350-codec/codec_reg does prints a list of registers up to e8 which is just a few bytes larger than the datasheet says the chip should be (0x00 to 0xe6).

I tried using a python program to play wav files, (works on my desktop computer), and I noticed that /dev/dsp does open, the mixers DO set volume levels, and nothing comes out. So -- the audio driver is not able to enable the sound amplifiers on it's own automatically.

There are no alsa sound files in /dev, nor are any alsa tools found on the embedded machine... so I assume Sony is strictly using OSS /dev/dsp and /dev/mixer.

There is only one other access point I can find to the ws8350: There IS a device driver /dev/wm8350.

That driver created by the source code in subdirectory wm8350/wm8350_reg.c ; in theory it should be able to read and write to all registers using ioctls() calls from a user space. However, something appears grossly wrong with it, for I wrote a test program to read the wm8350 registers... and most of the registers return error messages rather than allowing to be read, including the most pulic ID registers (0x00, 0x01) etc.

So, I'm quite stuck. Pointers, thoughts, hints, are quite desired.

Answer 1

I would like to change your question a little bit.

How does Linux ASOC (alsa system on chip) power management work?

I will answer this and then give some hints on using this specific chip.

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.. If I do a cat /sys/power/state it returns the word "mem" and nothing else. The file has permissions -rw-r--r--, so potentially it could be written -- but I don't know with what. The string "mem" does not exist anywhere in the source code for the wm8350pm drivers, so I don't even know if /sys/power/state is part of the source code.

You need to get an understanding of the Linux driver model. Hardware in Linux is structured like a tree. The rational is that things must be powered up/down in specific sequences. For instance, you should not power down the PCI bus controller before powering down the PCI peripherals. Linux builds a tree of hardware and each driver (code) and device (data/actual hardware) has specific call backs/function pointers which handle some specific tasks.

1. probe - Are you there? Determines actual hardware/device is present.
2. remove - Shuts down device. Module removal, power off, etc.
3. suspend - going to sleep.
4. resume - waking up.

Three and four may look interesting to you. Now, to read about what /sys/power/state is about. The text mem, means that suspend to memory is supported by your system. In this mode, Linux does these steps,

1. Find first lowest level active bus.
2. suspend devices on that bus.
3. suspend bus and de-activate.
4. If a bus is active go to step 1.
5. Set CPU to low power state (suspend to RAM).

This is not quite the full story. A few devices may support a wake-up. They will have extra call-backs to enable waking the system from sleep modes. Read the documentation to find out about this.

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That is general power management and driver/device structure. Now, how is the ASOC (alsa system on chip) structured?

There are typically three drivers/devices that get stitched together.

1. Codec - The wm8350 in your case. This includes audio amplifier drive circuitry and can include sound mixing and source controls. Supports digital to analog and analog to digital, typically through an i2s interface. The i2s is not the only interface. Usually a register bank is controlled through a secondary interface; i2c in the wm8350 case.
2. DAI - Refer to chapter 1.2.18.1 of the iMx31 reference manual; the hardware is called the SSI by Freescale. The next chapter on the AUDMUX is also useful to understand audio support on the iMx31/32.
3. Machine file - this is the board specific routing. It hooks the DAI to the codec and is the parent of both. It provides board clocking information and other specific configuration. For instance, it may use the AUDMUX to route the physical pins to the SSI block.
4. An i2c (or SPI) interface from the codec driver to send control commands to the coded chip. Some chips might uses a wacky i2s interface or something else for control (but not in your case).

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Now if you understood this, you will see that some features of the wm8350 seem to break the Linux model. The DAI interface can be stopped (digital audio), but the i2c interface must remain alive to program the registers related to the power functionality in the codec/PMIC (power management IC).

The latest WM8350 calls the IC a multi-function device and support was introduced in 2.6.35. The initial support may not have included the WM8350 features. Unfortunately, without some details on the layout of the Sony prs900 board, it would be difficult to know how to use the WM8350 PMIC functionality. The code will involve the iMx31 CPU, the WM8350, the i2c connection, and possibly some power supply circuitry.

For certain, you can just try echo mem > /sys/power/state and see what happens. If it works, you are lucky. The power/current consumption in sleep might not be optimal, but it will probably be hard to fix with the 2.6.23 kernel. You will want to look through the /sys directories for wake-up sources and possibly register these before issuing the suspend to memory command.

I can neither figure out how to read the battery/powerline status information, nor get the audio chip to play sound, etc ... although I have been studying the kernel modules for a while...

From the above discussions, the battery and powerline status will probably be found through another device. However, the pmic_reg file may actually give the status if things are connected properly on the board.

The audio chip will use ALSA. You need to use either alsamixer or the command line amixer to set up audio routes through the codec, so the DAI channel (PCM from iMx32) is routed and sent to the speaker. To minimize power consumption, things are usually turned off by default. The /dev/dsp files are just OSS compatibility. This configuration will support ALSA natively. You are better off to use ALSA if possible.

Donate to the OSF and get a tax receipt, if this was helpful enough.