Re: [PATCH 1/4] dt-bindings: opp: Introduce opp-bw-MBs bindings

From: Georgi Djakov <georgi.djakov@linaro.org>
To: Rob Herring <robh@kernel.org>
Cc: vireshk@kernel.org, sboyd@kernel.org, nm@ti.com,
	mark.rutland@arm.com, rjw@rjwysocki.net, jcrouse@codeaurora.org,
	vincent.guittot@linaro.org, bjorn.andersson@linaro.org,
	amit.kucheria@linaro.org, seansw@qti.qualcomm.com,
	daidavid1@codeaurora.org, evgreen@chromium.org,
	sibis@codeaurora.org, linux-pm@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH 1/4] dt-bindings: opp: Introduce opp-bw-MBs bindings
Date: Tue, 9 Apr 2019 17:39:08 +0300	[thread overview]
Message-ID: <6d918bd9-489c-89fa-733e-90a5dabdaa0c@linaro.org> (raw)
In-Reply-To: <20190328151255.GA5262@bogus>

Hi Rob,

On 3/28/19 17:12, Rob Herring wrote:
> On Wed, Mar 13, 2019 at 11:00:07AM +0200, Georgi Djakov wrote:
>> In addition to frequency and voltage, some devices may have bandwidth
>> requirements for their interconnect throughput - for example a CPU
>> or GPU may also need to increase or decrease their bandwidth to DDR
>> memory based on the current operating performance point.
>>
>> Extend the OPP tables with additional property to describe the bandwidth
>> needs of a device. The average and peak bandwidth values depend on the
>> hardware and its properties.
> 
> How would this work if you have 1 OPP (for the bus/interconnect/ddr) and 
> 2 devices with variable bandwidth needs? Or 'device' here means the 
> interconnect?

This is a property of the consumer devices and not of the bus. It's fine
for devices to have different bandwidth needs and to be connected to a
shared bus. In this case the framework knows the topology and can
determine which parts of the bus are shared and aggregate the traffic
accordingly.

>>
>> Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
>> ---
>>  Documentation/devicetree/bindings/opp/opp.txt | 45 +++++++++++++++++++
>>  1 file changed, 45 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
>> index 76b6c79604a5..fa598264615f 100644
>> --- a/Documentation/devicetree/bindings/opp/opp.txt
>> +++ b/Documentation/devicetree/bindings/opp/opp.txt
>> @@ -129,6 +129,9 @@ Optional properties:
>>  - opp-microamp-<name>: Named opp-microamp property. Similar to
>>    opp-microvolt-<name> property, but for microamp instead.
>>  
>> +- opp-bw-MBs: The interconnect bandwidth is specified with an array containing
>> +  the two integer values for average and peak bandwidth in megabytes per second.
> 
> -MBps would be better IMO. Either way, units should be documented in 
> property-units.txt.

Agree! Of course!

Thanks,
Georgi