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Tue, 20 Oct 2020 03:48:51 -0700 (PDT) Date: Tue, 20 Oct 2020 16:18:49 +0530 From: Viresh Kumar To: Nicola Mazzucato Cc: Lukasz Luba , Ionela Voinescu , Sudeep Holla , 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, chris.redpath@arm.com, morten.rasmussen@arm.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 2/2] [RFC] CPUFreq: Add support for cpu-perf-dependencies Message-ID: <20201020104849.xh4prj4az5islmpt@vireshk-i7> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716-391-311a52 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19-10-20, 14:36, Nicola Mazzucato wrote: > 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. Right, you need something like your patch here. -- viresh