Hi Thara,
On 9/17/2010 4:55 PM, Gopinath, Thara wrote:
From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx]
Sent: Thursday, September 16, 2010 8:58 PM
"Gopinath, Thara"<thara@xxxxxx> writes:
From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx]
Sent: Friday, September 03, 2010 5:12 AM
Thara Gopinath<thara@xxxxxx> writes:
This patch extends the device opp structure to contain
pointers to scale the operating rate of the
device and to retrieve the operating rate of the device.
This patch also adds the three new APIs in the opp layer
namely opp_set_rate that can be called to set a new operating
rate for a device, opp_get_rate that can be called to retrieve
the operating frequency for a device and opp_populate_rate_fns
to populte the device specific set_rate and get_rate API's.
The opp_set_rate and opp_get_rate does some routine error
checks and finally calls into the device specific set_rate
and get_rate APIs populated through opp_populate_rate_fns.
Signed-off-by: Thara Gopinath<thara@xxxxxx>
As I think about this more, I'm not sure the OPP layer is the right
layer for the get/set rate functions. The OPP layer is currently just
the data store for OPP data. To me, these set/get functions are better
associated directly with an omap_device instead of an OPP.
For instance, the new OPP APIs are a bit confusing in terms of OPPs.
e.g: opp_get_rate(). What is the "rate" of an OPP, and what's the
difference with opp_get_freq()?
What's really happening is the rate is being changed for a device, and
the need for specific hooks are at the device level, not the OPP level.
For example, this current approach would not scale if you needed
multiple devices in the same domain that each needed custom
set_rate/get_rate hooks.
So instead, what about adding custom hooks at the omap_device level?
They could be registered at omap_device_build() time in the device
specific code.
This is exactly what I had in my mind when I started implementing this.
But then Paul said hwmod or omap_device is not the place to keep it.
IIRC, Paul's concern was that *hwmod* was not the right place for this
(and I agree.) However, I think omap_device is the right place for
this.
Paul?
Also I do not want the set rate get rate APIs for devices that require
changes dividers in the PRCM clock module to be spread out in the
system. Makes it very very difficult to debug. If we agree to add the
set_rate and get_rate in the omap_device structure, I would like to
have one more API in the omap_device layer to register these APIs
device wise. Thus we can keep these set rate and get rate APIs in one
single file.
Agreed. And those functions should be in the respective
device-specific file, where the omap_device_build() etc are done for
that device.
Hello Kevin,
I basically agree with all your other suggestions except this. I do not
think device files are the correct place for this. For starters definitely mpu,
l3 and iva devices are not built from any device file. I do not like the idea
of device set rate APIs spread across different files.
I don't not understand the reason?
If we need to add specific device function for mpu, l3, or iva, we can
easily add a file to contain that.
BTW, thanks to work done by Santosh and Felipe we will probably soon
introduce a l3 driver that will allow to handle interconnect errors. We
will thus have a real device for l3 as well.
A device set_rate is clearly device specific. If a device will have to
play with its own internal dividers along with PRCM dividers, that code
still belong to the device.
I do not see the need nor the advantage to centralize that? You will
end-up with a huge file that every driver owners will have to hack in
order to add set_rate support for their device.
At device build time, IP with set_rate support will just add non-null
parameters to the omap_device_build(), et voila.
For the debug point of view, you can just add a new sysfs entry for
scalable devices that will allow you to track scalable device vs regular
ones.
Regards,
Benoit
What I am proposing is like we have opp_populate_rate_fns(which I have introduced)
we should have something like omap_device_populate_rate_fns. This can be then called
from one file to register the set_rate and get_rate APIs for all the relevant devices
for a Soc. This will be done through an init function. And the device specific
set_rate and get_rate can be implemented in this file. I am not sure which is
this file at this point of time. Maybe for OMAP3 opp3xxx_data.c or pm34xx.c. What
do you think about this?
Regards
Thara
Also if we move these hooks to omap_device struct we will need to
rename the current omap_device_set_rate (the main API) to
omap_device_scale and introduce a new omap_device_set_rate which just
finds out the omap device from the passed dev pointer and does a
od->set_rate. Similarly for get rate also.
Yes, that's what I was thinking.
Kevin
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