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

[Saravana Kannan]

On 03/01/2011 07:35 PM, Ryan Mallon wrote:
> 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.

Yes, my example was within a single SoC family. But since this is user 
space example, it doesn't matter if a single kernel can support multiple 
SoCs/SoC families. We could still have one userspace code that might 
want to support multiple SoC families.

Anyway, I think we are in agreement here. So, will stop discussing this 
point.

> > > > * 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.

True, but so many other things could be misused by stupid userspace 
programs. When there are legitimate usecases, I think we shouldn't 
prevent them just because we think a stupid userspace program could 
misuse it.

Again, although you might not be gung-ho about this, I think I have at 
least made you indifferent/mildly supportive to adding socinfo. If you 
don't mind, I would like to wait for others to chime in before 
continuing this discussion.

-Saravana
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