From: Viresh Kumar <viresh.kumar@linaro.org>
To: Nicola Mazzucato <nicola.mazzucato@arm.com>
Cc: devicetree@vger.kernel.org, linux-pm@vger.kernel.org,
vireshk@kernel.org, daniel.lezcano@linaro.org, rjw@rjwysocki.net,
linux-kernel@vger.kernel.org, robh+dt@kernel.org,
linux-arm-kernel@lists.infradead.org,
Sudeep Holla <sudeep.holla@arm.com>,
chris.redpath@arm.com, Ionela Voinescu <ionela.voinescu@arm.com>,
morten.rasmussen@arm.com, Lukasz Luba <lukasz.luba@arm.com>
Subject: Re: [PATCH v2 2/2] [RFC] CPUFreq: Add support for cpu-perf-dependencies
Date: Mon, 19 Oct 2020 15:16:33 +0530 [thread overview]
Message-ID: <20201019094633.m3yvxurfm2xwsb6a@vireshk-i7> (raw)
In-Reply-To: <503af305-77a4-964a-ed17-8df8b4e3a546@arm.com>
On 19-10-20, 09:50, Nicola Mazzucato wrote:
> Hi Viresh,
>
> thank you for your suggestion on using 'opp-shared'.
> I think it could work for most of the cases we explained earlier.
>
> Summarising, there are two parts of this entire proposal:
> 1) where/how to get the information: now we are focusing on taking advantage of
> 'opp-shared' within an empty opp table
> 2) and how/where this information will be consumed
>
> Further details below:
>
> 1) a CPUFreq driver that takes the OPPs from firmware, can call
> dev_pm_opp_of_get_sharing_cpus like you suggested. When doing so, a provided
> cpumaksk will be populated with the corresponding cpus that share the same
> (empty) table opp in DT.
> All good so far.
Great.
> The current opp core is not expecting an empty table and therefore some errors
> are thrown when this happens.
> Since we are now allowing this corner-case, I am presenting below where I think
> some minor corrections may be needed:
>
> --- a/drivers/opp/of.c
> +++ b/drivers/opp/of.c
> @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
> struct device_node *required_np, *np;
> int count, i;
>
> /* Traversing the first OPP node is all we need */
> np = of_get_next_available_child(opp_np, NULL);
> if (!np) {
> - dev_err(dev, "Empty OPP table\n");
> + dev_warn(dev, "Empty OPP table\n");
> +
> + /*
> + * With empty table we remove shared_opp. This is to leave the
> + * responsibility to decide which opp are shared to the opp users
> + */
> + opp_table->shared_opp = OPP_TABLE_ACCESS_EXCLUSIVE;
> +
> return;
> }
>
> @@ int dev_pm_opp_of_find_icc_paths(struct device *dev,
> int ret, i, count, num_paths;
> struct icc_path **paths;
>
> ret = _bandwidth_supported(dev, opp_table);
> - if (ret <= 0)
> + if (ret == -EINVAL)
> + return 0; /* Empty OPP table is a valid corner-case, let's not
> fail */
> + else if (ret <= 0)
> return ret;
>
> The above are not 'strictly' necessary to achieve the intended goal, but they
> make clearer that an empty table is now allowed and not an error anymore.
> What it is your point of view on this?
Why is this stuff getting called in your case ? We shouldn't be trying
to create an OPP table here and it should still be an error in the
code if we are asked to parse an empty OPP table.
> In addition, I think it would also be appropriate to update the documentation
> (Documentation/devicetree/bindings/opp/opp.txt) to reflect this new case
> (required properties etc).
> Any different thoughts?
Yes, this needs a small update in the required-opps section.
> 2) Once the driver gets the 'performance dependencies' by
> dev_pm_opp_of_get_sharing_cpus(), this information will have to be shared with
> EAS, thermal, etc.. The natural way to do so would be to add a new cpumask like
> I proposed in this RFC.
> I see this as an improvement for the whole subsystem and a scalable choice since
> we can unambiguously provide the correct information to whoever needs it, given
> that we don't enforce "hw dependencies" for related_cpus.
> The changes would be trivial (it's in the original RFC).
> On the other hand, we can't unload this h/w detail into related_cpus IMO as we
> are dealing with per-cpu systems in this context.
> Hope it makes sense?
I will have another look at this stuff, honestly I haven't looked at
this in detail yet. But I do understand that we can't really use
related-cpu here without changing its earlier meaning.
--
viresh
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next prev parent reply other threads:[~2020-10-19 9:48 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 9:53 [PATCH v2 0/2] CPUFreq: Add support for cpu performance dependencies Nicola Mazzucato
2020-09-24 9:53 ` [PATCH v2 1/2] dt-bindings: arm: Add devicetree binding for cpu-performance-dependencies Nicola Mazzucato
2020-10-08 13:42 ` Ionela Voinescu
2020-09-24 9:53 ` [PATCH v2 2/2] [RFC] CPUFreq: Add support for cpu-perf-dependencies Nicola Mazzucato
2020-10-06 7:19 ` Viresh Kumar
2020-10-07 12:58 ` Nicola Mazzucato
2020-10-08 11:02 ` Viresh Kumar
2020-10-08 15:03 ` Ionela Voinescu
2020-10-08 15:57 ` Rafael J. Wysocki
2020-10-08 17:08 ` Ionela Voinescu
2020-10-12 16:06 ` Sudeep Holla
2020-10-08 16:00 ` Nicola Mazzucato
2020-10-09 5:39 ` Viresh Kumar
2020-10-09 11:10 ` Nicola Mazzucato
2020-10-09 11:17 ` Viresh Kumar
2020-10-09 14:01 ` Rob Herring
2020-10-09 15:28 ` Nicola Mazzucato
2020-10-12 4:19 ` Viresh Kumar
2020-10-12 10:22 ` Lukasz Luba
2020-10-12 10:50 ` Rafael J. Wysocki
2020-10-12 11:05 ` Lukasz Luba
2020-10-12 10:59 ` Ionela Voinescu
2020-10-12 13:48 ` Lukasz Luba
2020-10-12 16:30 ` Ionela Voinescu
2020-10-12 18:19 ` Lukasz Luba
2020-10-12 22:01 ` Ionela Voinescu
2020-10-13 11:53 ` Rafael J. Wysocki
2020-10-13 12:39 ` Ionela Voinescu
2020-10-15 15:56 ` Rafael J. Wysocki
2020-10-15 18:38 ` Ionela Voinescu
2020-10-12 13:59 ` Rob Herring
2020-10-12 16:02 ` Sudeep Holla
2020-10-12 15:54 ` Sudeep Holla
2020-10-12 15:49 ` Sudeep Holla
2020-10-12 16:52 ` Ionela Voinescu
2020-10-12 17:18 ` Lukasz Luba
2020-10-14 4:25 ` Viresh Kumar
2020-10-14 9:11 ` Lukasz Luba
2020-10-19 8:50 ` Nicola Mazzucato
2020-10-19 9:46 ` Viresh Kumar [this message]
2020-10-19 13:36 ` Nicola Mazzucato
2020-10-20 10:48 ` Viresh Kumar
2020-10-13 13:53 ` Lukasz Luba
2020-10-14 4:20 ` Viresh Kumar
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