linux-arm-kernel.lists.infradead.org archive mirror
 help / color / mirror / Atom feed
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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20201019094633.m3yvxurfm2xwsb6a@vireshk-i7 \
    --to=viresh.kumar@linaro.org \
    --cc=chris.redpath@arm.com \
    --cc=daniel.lezcano@linaro.org \
    --cc=devicetree@vger.kernel.org \
    --cc=ionela.voinescu@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=lukasz.luba@arm.com \
    --cc=morten.rasmussen@arm.com \
    --cc=nicola.mazzucato@arm.com \
    --cc=rjw@rjwysocki.net \
    --cc=robh+dt@kernel.org \
    --cc=sudeep.holla@arm.com \
    --cc=vireshk@kernel.org \
    --subject='Re: [PATCH v2 2/2] [RFC] CPUFreq: Add support for cpu-perf-dependencies' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).