Re: [PATCH v9 2/8] dt-bindings: Introduce interconnect binding

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On 10/02/2018 04:17 AM, Sudeep Holla wrote:
On Mon, Oct 01, 2018 at 04:49:32PM -0700, Saravana Kannan wrote:
On 09/26/2018 07:48 AM, Sudeep Holla wrote:
On Wed, Sep 26, 2018 at 05:42:15PM +0300, Georgi Djakov wrote:
Hi Rob,

Thanks for the comments!

On 09/25/2018 09:02 PM, Rob Herring wrote:
On Fri, Aug 31, 2018 at 05:01:45PM +0300, Georgi Djakov wrote:
This binding is intended to represent the relations between the interconnect
controllers (providers) and consumer device nodes. It will allow creating links
between consumers and interconnect paths (exposed by interconnect providers).
As I mentioned in person, I want to see other SoC families using this
before accepting. They don't have to be ready for upstream, but WIP
patches or even just a "yes, this works for us and we're going to use
this binding on X".
Other than the 3 Qualcomm SoCs (msm8916, msm8996, sdm845) that are
currently using this binding, there is ongoing work from at least two
other vendors that would be using this same binding. I will check on
what is their progress so far.

Also, I think the QCom GPU use of this should be fully sorted out. Or
more generically how this fits into OPP binding which seems to be never
ending extended...
I see this as a further step. It could be OPP binding which include
bandwidth values or some separate DT property. Jordan has already
proposed something, do you have any initial comments on that?
I am curious as how this fits into new systems which have firmware driven
CPUFreq and other DVFS. I would like to avoid using this in such systems
and leave it upto the firmware to scale the bus/interconnect based on the
other components that are connected to it and active.

You've made the same point multiple times across different patch sets. Not
all FW can do arbitrary functions. A lot of them are very limited in their
capabilities. So, as much as you and I would like to let the FW do the work,
it's not always possible. So, in those cases, we do need to have support for
the kernel scaling the interconnects correctly. Hopefully this clears up
your questions about FW capabilities.
Yes, I do understand I have made the same point multiple time and it's
intentional. We need to get the fragmented f/w support story fixed.
Different ARM vendors are doing different things in f/w and ARM sees the
same fragmentation story as before. We have come up with new specification
and my annoying multiple emails are just to constantly remind the same.

I do understand we have existing implementations to consider, but fixing
the functionality in arbitrary way is not a good design and it better
to get them fixed for future.

I believe the fragmentation you are referring to is  in the interface/communication protocol. I see the benefit of standardizing that as long as the standard actually turns out to be good. But that's completely separate from what the FW can/can't do. Asking to standardize what the FW can/can't do doesn't seem realistic as each chip vendor will have different priorities - power, performance, cost, chip area, etc. It's the conflation of these separate topics that doesn't help IMHO.

-Saravana


--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project




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