Hi Viresh, Rafael, > On 29 May 2013 03:18, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > On Tuesday, May 28, 2013 03:26:25 PM Lukasz Majewski wrote: > >> Hi Viresh, Rafael, > >> > >> > On Tuesday, May 28, 2013 03:14:26 PM Viresh Kumar wrote: > > >> > I'm not sure about that. On x86 boost will be used with all > >> > governors if enabled (as currently defined in acpi-cpufreq). > >> > >> All governors can benefit from the overclocking code. > > Yeah. > > >> > Also it looks like this depends on the driver too, because if the > >> > driver doesn't have "turbo" frequencies, the governor won't be > >> > able use "turbo" anyway. > > Yes. > > >> > So first, it would make sense to use a per-driver "boost" > >> > attribute indicating whether or not the given driver should > >> > present any "turbo" frequencies to the governor. > > @Lukasz: So, you need to add another field in struct cpufreq_driver, > which will be called "turbo_mode" or something better. This is my intention - to extend cpufreq_driver structure. When turbo_mode=1, then we will export knobs to sysfs. For ARM, it is also convenient to define proper attribute at device tree, per-board source file. It will be parsed at cpufreq driver and set turbo_mode accordingly. > > >> Now I'm using a device tree's cpufreq section (defined at > >> exynos4412-redwood.dts) with overclocking = "okay" attribute > >> defined. Then, on this basis, we could decide at cpufreq init time > >> if we will export any overclocking related sysfs entries (or init > >> overclocking at all). It would assure clearer code. > > > > Well, what about users? Don't you want them to be able to decide > > whether or not to use "turbo"? > > I believe Lukasz was saying that we can have two levels of enabling > it.. Firstly the driver can say if it supports turbo_mode or not and > so will register cpufreq_driver with appropriate parameters.. > > Now if turbo_mode == true, then sysfs entry will be created by cpufreq > core which users can enable/disable... > Yes, this is the point. Sorry for blur description. > And this is what I had in mind too. > > >> I think that global cpufreq device tree attribute shall be defined. > > > > What do you mean by "device tree attribute"? If you mean FDTs as > > used by ARM for system configuration description, that wouldn't be > > portable, because DTs aren't used for that on the (majority of) x86 > > systems. > > So, drivers should pass correct value in boost_mode in struct > cpufreq_driver. They get it from DT or is hard coded doesn't matter > at all to the core. But yes getting a single name for DT bindings > would be good. We should use the same name at that place too: > turbo_mode > Yes, this is my goal. For prototype (on which I'm now working) I've used overclock attribute. But, I will change its name to turbo_mode. > >> The overclocking will be an integral part of the cpufreq framework. > > > > Well, to be precise, I was thinking about moving the management of > > the /sys/devices/system/cpu/cpufreq/boost attribute from > > acpi-cpufreq to the code so that other drivers may use it too. > > Does that make sense to you? > > Obviously yes. The sysfs related code from acpi-cpufreq should be > moved to cpufreq.c and will be functional once cpufreq_driver has > boost_mode set as true. I also agree. Moreover, I think that there should be only one set of "boost" sysfs entries either it is supported by HW (Intel) or SW (ARM). I can think of two "basic" one: - max_turbo_freq (ro) - turbo_mode/boost (rw) But I cannot figure out where those entries shall be finally placed [*]: - /sys/devices/system/cpu/cpuX/cpufreq/ or - /sys/devices/system/cpu/cpufreq/boost Second option would be better, if we assume that boost is a global option - as at Intel (I might be wrong here...) and ARM exynos4 SoC. On the other hand first option would be used with systems, where per-core (or core sets) frequency setting is possible (b.L, Snapdragon S4) > > >> > Second, I'm not sure if an additional knob for the governor is > >> > necessary. It may just use the turbo frequencies if available > >> > (and if the governor cannot use them, it simply won't use them). > >> > >> I cannot agree. It is welcome to be able to enable/disable the > >> feature when needed. Turbo frequencies shall not be "available" > >> for use all the time. > > Yes, you can disable that from userspace once your driver said: "I > support turbo mode".. To sum up - the idea is as follow: 1. cpufreq_driver exports turbo_mode=1 when it supports overclocking (this support can be hardcoded or read from device tree) 2. Then proper entries are exported to sysfs. 3. User via sysfs (at [*]) can enable/disable the feature on demand -- Best regards, Lukasz Majewski Samsung R&D Poland (SRPOL) | Linux Platform Group -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
