Hi Thara,
On 9/29/2010 1:16 PM, Gopinath, Thara wrote:
-----Original Message-----
From: Cousson, Benoit
Sent: Saturday, September 18, 2010 3:43 PM
To: Gopinath, Thara
Cc: Kevin Hilman; Paul Walmsley; linux-omap@xxxxxxxxxxxxxxx; Sripathy,
Vishwanath; Sawant, Anand
Subject: Re: [PATCH 05/13] OMAP: Introduce device specific set rate and get
rate in device opp structures.
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.
Hello Benoit/Kevin,
Most of the devices need not scale any internal dividers. For devices that
need to scale internal dividers, I agree that the set_rate and get_rate should come from the devices file. But for other devices that involve only PRCM dividers, I do not think they should be bothered with implementing these APIs and maintaining them.
But why? For dividers under PRCM control, we do have clock nodes to
control them, so device can still use them.
I'm still missing your point about centralizing that.
Benoit
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