Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755470AbcJYVNy (ORCPT ); Tue, 25 Oct 2016 17:13:54 -0400 Received: from comal.ext.ti.com ([198.47.26.152]:48883 "EHLO comal.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752366AbcJYVNu (ORCPT ); Tue, 25 Oct 2016 17:13:50 -0400 Subject: Re: [PATCH V2 0/8] PM / OPP: Multiple regulator support To: Viresh Kumar References: <41a8b4a1-94d3-e086-a328-495f69815d1c@ti.com> <20161024042659.GD24749@vireshk-i7> CC: "Rafael J. Wysocki" , Rafael Wysocki , Nishanth Menon , Stephen Boyd , Lists linaro-kernel , Linux PM , Linux Kernel Mailing List , Vincent Guittot , Rob Herring , Mark Brown From: Dave Gerlach Message-ID: <4059f5a9-5308-8a5e-827b-4f822d9049d2@ti.com> Date: Tue, 25 Oct 2016 16:13:38 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20161024042659.GD24749@vireshk-i7> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [128.247.83.19] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5511 Lines: 130 Hi, On 10/23/2016 11:26 PM, Viresh Kumar wrote: > On 23-10-16, 20:08, Dave Gerlach wrote: >> Overall this series looks good to me apart from a few small things. Most >> importantly I was able to get a working implementation using two regulators >> on ti dra7xx platform with proper sequencing built on top of this series. We >> have cpu regulator and Adaptive body bias (abb) regulator that must be >> scaled in a certain order before or after clock scaling and I was able to >> implement a rough custom set_rate to perform this and ran some dvfs stress >> tests that all worked fine. > > Thanks for testing it buddy. > >> First comment, I think the platform specific set_rate is a good place to >> hook in for adaptive voltage scaling as well. I was able to implement TI >> Class0 AVS in the same code by using the requested transition voltage as a >> reference and programming AVS voltage using that, along with scaling the >> additional regulators in sequence (the original multi regulator >> functionality). > > Hmm, interesting.. > >> I would think some people would want to use this even with >> single regulator platforms, no? > > Maybe, but I would like to see such user code first. It may be possible to > handle much of AVS stuff in core so that everyone isn't required to do it. Ok, I think it would be a logical next step to look at once this series gets accepted. For now, the particular implementation I did just looks up an optimized value for the requested voltage from a register and programs the optimal value instead of the requested voltage. > >> This raises some concerns about dependencies/probe sequencing. Right now we >> just need to make sure the cpufreq-dt driver probes after we have called >> _set_regulators, but if our platform code fails cpufreq-dt currently will >> treat this as no regulator needed for the platform and operate without one, >> which will likely hang the system. Is there a good way to to guarantee this >> doesn't happen? My main concern is that if we plan to provide a platform >> specific set-rate function, we should have a way to indicate this and >> prevent things from progressing if it isn't yet ready. >> >> Again, overall I think it solves the multi regulator problem, and it works >> well for AVS as well. For the series: >> >> Tested-by: Dave Gerlach > > Thanks. > > For the concern you shared about, does the below patch fix it ? I will include > that in V3 then. I think what you have shared below is a good safety check but if I rename the regulator properties in the DT for the cpu (to vdd and vbb, meaning cpufreq detects no regulator) and do *not* call dev_pm_opp_set_regulators before cpufreq-dt probes we fail before we even get to that point: [16.946] cpu cpu0: opp_parse_supplies: Invalid number of elements in opp-microvolt property (6) with supplies (1) [16.967] cpu cpu0: _of_add_opp_table_v2: Failed to add OPP, -22 [16.982] cpu cpu0: dev_pm_opp_get_opp_count: OPP table not found (-19) [16.982] cpu cpu0: OPP table is not ready, deferring probe This failure is because opp_parse_supplies assumes a count of 1 regulator if no regulators at all are present and then hard fails if too many voltages have been passed for each OPP. It seems we need a check much earlier similar to what you suggested below to allow us to defer if an OPP has supplied voltages but no regulator has been registered with the system. I think this is reasonable even for the 1 regulator case, no? If we have passed voltages then we presumably are hoping to use them with a regulator, and if no regulators are present, OPP framework should defer. cpufreq-dt won't handle this properly as is, but now that the opp core is evolving perhaps it makes sense to modify the resources_available check slightly to rely on the OPP core rather than just a dummy regulator_get_optional to see if the regulator is ready. Regards, Dave > > -------------------------8<------------------------- > > From: Viresh Kumar > Date: Mon, 24 Oct 2016 09:45:30 +0530 > Subject: [PATCH] PM / OPP: Don't assume platform doesn't have regulators > > If the regulators aren't set explicitly by the platform, the OPP core > assumes that the platform doesn't have any regulator and uses the > clk-only callback. > > If the platform failed to register a regulator with the core, then this > can turn out to be a dangerous assumption as the OPP core will try to > change clk without changing regulators. > > Handle that properly by making sure that the DT didn't had any entries > for supply voltages as well. > > Signed-off-by: Viresh Kumar > --- > drivers/base/power/opp/core.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/drivers/base/power/opp/core.c b/drivers/base/power/opp/core.c > index b69908b74ed6..fb4250532180 100644 > --- a/drivers/base/power/opp/core.c > +++ b/drivers/base/power/opp/core.c > @@ -737,7 +737,17 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq) > > /* Only frequency scaling */ > if (!regulators) { > - rcu_read_unlock(); > + /* > + * DT contained supply ratings? Consider platform failed to set > + * regulators. > + */ > + if (unlikely(opp->supplies[0].u_volt)) { > + rcu_read_unlock(); > + dev_err(dev, "%s: Regulator not registered with OPP core\n", > + __func__); > + return -EINVAL; > + } > + > return _generic_opp_set_rate_clk_only(dev, clk, old_freq, freq); > } > >