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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kUVJo-000186-UD; Mon, 19 Oct 2020 13:35:20 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kUVJm-00017c-3q for linux-arm-kernel@lists.infradead.org; Mon, 19 Oct 2020 13:35:19 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 212E6D6E; Mon, 19 Oct 2020 06:35:15 -0700 (PDT) Received: from [10.57.14.99] (unknown [10.57.14.99]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id ECC563F719; Mon, 19 Oct 2020 06:35:12 -0700 (PDT) Subject: Re: [PATCH v2 2/2] [RFC] CPUFreq: Add support for cpu-perf-dependencies To: Viresh Kumar References: <2417d7b5-bc58-fa30-192c-e5991ec22ce0@arm.com> <20201008110241.dcyxdtqqj7slwmnc@vireshk-i7> <20201008150317.GB20268@arm.com> <56846759-e3a6-9471-827d-27af0c3d410d@arm.com> <20201009053921.pkq4pcyrv4r7ylzu@vireshk-i7> <20201012154915.GD16519@bogus> <20201012165219.GA3573@arm.com> <17819d4d-9e7e-9a38-4227-d0d10a0749f1@arm.com> <20201014042531.r7iykzygkvmpsqck@vireshk-i7> <503af305-77a4-964a-ed17-8df8b4e3a546@arm.com> <20201019094633.m3yvxurfm2xwsb6a@vireshk-i7> From: Nicola Mazzucato Message-ID: Date: Mon, 19 Oct 2020 14:36:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20201019094633.m3yvxurfm2xwsb6a@vireshk-i7> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201019_093518_270581_7F63301D X-CRM114-Status: GOOD ( 36.14 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 , chris.redpath@arm.com, Ionela Voinescu , morten.rasmussen@arm.com, Lukasz Luba Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Viresh, On 10/19/20 10:46 AM, Viresh Kumar wrote: > 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. A driver that gets a set of opp-points from f/w needs to add them to each device. To do so, it will call dev_pm_opp_add(). If an opp_table struct for this device is not found, one will be created and the opp-point will be added to it. When allocation a new opp_table the opp will try to initialise it by parsing the values in DT. It will also try to find_icc_paths. Everything happens silently if we don't have a table in DT. > >> 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. Cool, I'll sketch something in the next version. > >> 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. Sure. thanks > Hope it helps Best regards Nicola _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel