Re: 2/5 System Device Driver Modifications


Boie, Andrew P
 

On Fri, 2016-03-11 at 19:02 +0000, Kalowsky, Daniel wrote:
-----Original Message-----
From: Boie, Andrew P [mailto:andrew.p.boie(a)intel.com]
Sent: Friday, March 11, 2016 9:24 AM
To: Thomas, Ramesh <ramesh.thomas(a)intel.com>;
devel(a)lists.zephyrproject.org
Subject: [devel] Re: 2/5 System Device Driver Modifications


2) Provide a name recognized by the device_get_binding() function, this
includes what are currently thought to be drivers such as timers, IOAPIC,
and
LOAPIC.
Why do you need this for the LOAPIC/IOAPIC?
All its functions are private to the kernel and do not require a device pointer.
Please provide a specific example on where you would need to run
device_get_binding() specifically for the APIC.
device_get_binding() is *slow*. It does a linear search + strcmp(). Use it
sparingly.
We agree that the device_get_binding is slow. We'd rather not depend upon it,
which is why we had suggested the addition of a routine to get the start and
end of the device list and allow the PMA to parse this list once at
initialization to figure out what is or is not needed for power
policies.
If you just need to iterate over all devices this code does the job:

struct device *info;

for (info = __device_init_start; info != __device_init_end; info++) {
/* do stuff */
}

Could add an API to nanokernel/device.c to take a function(struct device
*d) as a parameter and apply to all of them so that the private
__device_init_* symbols don't need to be public.

If we go with that solution, pushing all policy decisions to the PMA,
we need to be able to properly identify the devices as that list is
parsed. Currently several devices, like IOAPIC and LOAPIC, have no
name or function to identify them and make this route difficult.
I'm still confused. Does the PMA need to only apply .suspend/.resume
operations to a subset of all devices? Some examples/usecases would
help...


--
Andrew Boie
Staff Engineer - EOS Zephyr
Intel Open Source Technology Center

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