[RFC PATCHv1 1/2] Export SoC info through sysfs

[Linus Walleij]

2011/3/9 Arnd Bergmann <arnd at arndb.de>:
> On Wednesday 09 March 2011 17:59:20 Maxime Coquelin wrote:
>> Common base to export System-on-Chip related informations through sysfs.
>>
>> Creation of a "soc" directory under /sys/devices/system/.
>
> Why under system?
>
> As far as I can tell, the SOC already exists as a platform device
> under /sys/devices/platform,

This is from U8500:

/sys/devices/platform ls

ab8500-i2c.0   gpio.0         gpio.5         nmk-i2c.0      uevent
arm-pmu.0      gpio.1         gpio.6         nmk-i2c.1
cpufreq-u8500  gpio.2         gpio.7         nmk-i2c.2
dma40.0        gpio.3         gpio.8         nmk-i2c.3
gpio-keys.0    gpio.4         musb-ux500.0   reg-dummy

In our case the above are platform_device:s and also MFD cells,
children of I2C devices (anything prefixed with ab8500-*) which
have absolutely *nothing* to do with what is inside the SoC.

Further these SoC entries don't even have a device of *any* kind tied
to them. It's just hooks reading binary right out of some extremely
system-specific memory locations and producing matching strings.

"platform" means "platform bus" in this context, does it not?
So your reasoning is that since on SoC:s there is one dominant
bus called the platform bus that should also hold a reference to the
SoC-specific stuff.

On the ARM Versatiles this isn't even true: there the dominant
bus is the AMBA (PrimeCell) bus, and the U8500 uses a mixture
of both. AMBA devices incidentally turn up as entries directly
in /sys/devices:

/sys/devices ls
platform   sdi0       sdi4       system     uart1      virtual
rtc-pl031  sdi2       ssp0       uart0      uart2

The sdi, uart & rtc you see here are AMBA devices.

So platform is just the platform bus, not the, you know,
*platform*. There are competing on-chip busses not just one.

So standardizing the location here,
/sys/devices/system contain these more neutral things:

/sys/devices/system ls
clocksource  cpu          timekeeping  timer

IMHO socinfo fits here, just as it is in the patch.

This might be a bit of bikeshed-color discussion but I
happen to like this black color sooooo much...

Just my €0.01
Linus Walleij