Re: Info on LDM, domain system and SOCs

[Igor Stoppa <igor.stoppa@nokia.com>]

Hi,
On Mon, 2007-09-24 at 11:14 +0000, ext Francesco VIRLINZI wrote:
> Amit Kucheria ha scritto:
> > On 9/10/07, Francesco VIRLINZI <francesco.virlinzi@st.com> wrote:
> >   
> >> If you mean the <include/linux/clk.h>, I already saw it.
> >> I think it's good but it isn't enough.
> >> I want track also the devices on a clock to be able to notify (for each
> >> device) if a clock changes.
> >>     
> >
> > You should propose these changes to the clock framework. Designing a
> > new framework is unlikely to be accepted in the kernel easily since a
> > lot of platforms are using the clock framework already.
> >   
> Hi
> I'm sorry but this is really what I don't want to do.
> I think the problem is really this.
> 
> In the kernel there are a several clock struct... one for each 
> architecture...

The clk fw interface is common; implementation is of course
platform/architecture specific

> A lot of them have no relation with the linux driver model... and they 
> aren't showed under /sys/...
> This means there is a physical clock network not aware by the kernel.
> 
> For this reason I don't want "write-a-new" or "extend-an-existent" clock 
> framework..
> 
> I'm working on a domain framework arch independent (a kind of ancestor 
> of all the clock framework)
>  able to track the domain relationship and also the device-on-domain 
> relationship.
> This framework should go under <root>/drivers/base/...
> The basic idea is to create a base code for all the architectures to 
> simplify (I hope)
>  the clocks managements in the SOCs.

Integration of power domains in the LDM could be easily obtained by
modelling a buf for each power domain.


> For example in my platform I can do something like:
> 
> # ls /sys/domains/pll1_clk/comms_clk/devices/
> # ssc-0  ssc-1  ssc-2
> 
> This means in my platform there are
>  - a parent clock pll1_clk
>  - a child clock comms_clk
>  - three devices (ssc-0 ssc-1 ssc-2) under comms_clk

How is this different from the current cases?

> And this information are available in user space (I think this information
>  could help a power manager in user space)

I can hardly see a userspace power manager be able to handle low
latencies involved in clock gating. Unless you are referring to
unlocking vs. enabling bypass mode for PLLs when their usecount reaches
0.



 
-- 
Cheers, Igor

Igor Stoppa <igor.stoppa@nokia.com>
(Nokia Multimedia - CP - OSSO / Helsinki, Finland)