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


    Bluewater Systems Ltd - ARM Technology Solution Centre

    Ryan Mallon 5 Amuri Park, 404 Barbadoes St PO Box 13 889, Christchurch 8013 New Zealand
    Phone: +64 3 3779127 Freecall: Australia 1800 148 751
    Fax: +64 3 3779135 USA 1800 261 2934

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