Re: [PATCHv5 0/3] Introduce the /proc/socinfo and use it to export OMAP data

[Ryan Mallon <ryan@bluewatersys.com>]

On 03/02/2011 04:21 PM, Saravana Kannan wrote:
> On 03/01/2011 07:11 PM, Ryan Mallon wrote:
>> On 03/02/2011 03:55 PM, Saravana Kannan wrote:
>>> On 03/01/2011 06:41 PM, Ryan Mallon wrote:
>>>> On 03/02/2011 03:23 PM, Saravana Kannan wrote:
>>>>> I don't have any attachment to the "arch" file suggestion. If there
>>>>> is a
>>>>> better solution to identify the different implementations of socinfo
>>>>> without having to maintain some "unique id" list in the kernel,
>>>>> then I'm
>>>>> all for it. But cpuinfo is not it.
>>>>
>>>> Sorry I am confusing the 'arch' and 'mach' bits here. I definitely have
>>>> an objection to having an 'arch' file (i.e. ARM). A 'mach' (i.e. omap)
>>>> file makes a bit more sense, but should probably be called 'mach'
>>>> rather
>>>> than 'arch' to avoid this confusion :-).
>>>
>>> Sorry for the confusion. Sure, I don't care much for the filename as
>>> long as we can all agree on it. I care more about the content of the
>>> file (using names very close to xxxx in mach-xxxx). I like "soc-family"
>>> better since it's generic enough to not force, say omap3 and omap4, to
>>> report different values.
>>>
>>> Linus Walleij, Eduardo, Maxime, Andrei,
>>>
>>> Would like to hear your opinion on the file name (soc-family vs. mach vs
>>> <somethingelse>) and the path /sys/devices/system/soc/.
>>
>> 'family' sounds good. I don't think we need the 'soc-' prefix on
>> filenames if they are already in /sys/devices/system/soc/.
> 
> Makes sense. We can drop the soc- prefix. So the contenders left: family
> vs <somethingelse>. Would still be nice if the other folks chime in.
> 
>>> If we settle on this, may be it would be easier to get this through.
>>>
>>>> I still think it is a solution in search of a problem though. What
>>>> userspace programs need to know what specific SoC they are on? My
>>>> feeling is that if userspace needs to know this information, then it is
>>>> probably dicking around with things that should be managed by the
>>>> kernel. Differences in available peripherals, etc can be determined by
>>>> looking at existing sysfs files.
>>>
>>> I certainly have seen several use cases. Couple of easy examples:
>>>
>>> * A lot of test scripts would find this very useful. For example, some
>>> clock (present is all/most MSMs) shouldn't be tested on some SOCs as it
>>> would lock up the system if you try to turn it off while the CPU is
>>> running.
>>
>> I don't follow here. Do you mean a struct clk clock or something else?
>> Why is userspace allowed to disable a clock which will effectively hang
>> the system? :-).
> 
> Ah, sorry. Didn't give enough details. To give some context, I manage
> the clock stuff for MSM. The MSM clock driver exports clock control thru
> debugfs. We have test scripts that bang the clocks to test them. Each
> SoC has a different set of "touch me and you die" clocks that the test
> script shouldn't mess with. This socinfo would be useful for those test
> cases.

Ah, okay. This is still within a single SoC family though since we don't
yet (AFAIK) support mutliple SoCs in a single kernel.

>>> * Some of the user space tools might want to report different "product
>>> id/type" (nothing to do with USB, etc) depending on what SOC it is
>>> running on.
>>
>> This makes more sense. It would actually be useful for custom USB
>> devices (gadget) which can be done from user space.
> 
> Hmm... didn't know USB devices/gadgets could be handled from userspace.

The gadgetfs driver allows for writing custom usb device
implementations. The SoC info could be used to set the USB
vendor/product id. Again, I see this more useful within the SoC family
(ie at91sam9260 vs at91sam9263) rather than between families. From an
embedded perspective at least, I think it is unlikely for an application
to need to work on multiple SoC families.

The only real objection I have to adding the SoC family information is
basically to discourage it being abused by userspace. I can see it being
useful in debug situations, but I can also see stupid userspace
applications explicitly testing for some particular SoC, rather than
more correctly (IMHO) checking for presence of certain drivers etc.

~Ryan

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