On 07/22/2013 07:25 AM, Eduardo Valentin wrote: > Hello Grant and Rob, > > (Resending, as I got a message saying: > <devicetree-discuss@xxxxxxxxxxxxxxxx>: Recipient address rejected: > User has moved to devicetree at vger.kernel.org) > > I am writing this email to you specifically to ask your technical > assessment with respect to representing device thermal limits as > device tree nodes. I am proposing to introduce device tree nodes to > describe these limits as thermal zones, their composition and their > relations with cooling devices and other thermal zones (thermal > data). Given: https://lkml.org/lkml/2013/7/20/69 [PATCH 3/3] MAINTAINERS: Refactor device tree maintainership I'm explicitly CCing a few people besides Grant/Rob, and qouting the whole email. >From my perspective, the concept of including thermal limits in DT seems reasonable, although I haven't looked at the proposed binding itself in detail yet. > As you should know, device thermal limits are part of hardware > specification. Considering your board layout, mechanics, power > dissipation and composition of ICs, etc, that will impose thermal > requirements on your system, and infringing these limits can lead > to device damage, device life time reduction or even end user harm. > Thus, the thermal data help to describe the hardware limits and > what needs to be done if those limits are crosses, as part of your > board design and non-functional requirements. Obviously that is > very dependent on your hardware, and not all of them will have > these non-functional requirements. Besides, describing these limits > has *nothing* to do with how you actually find these limits. > > In any case, there is a need to properly represent these > requirements and I am proposing to have this representation in > device tree. There were already couple of counter-arguments > claiming this is actually about configuration and performance > profile description. But I still stand against these two readings > of this proposal and again state that if one interprets it as > configuration or performance profile, that is a mis-understanding > [0]. Let me state it clear (again [1]), my proposal is to describe > hardware thermal limits, because these limits are part of a > hardware specification; representing in device tree would not > infringe the original purpose of this data structure ("The Device > Tree is a data structure for describing hardware."[2]). > > Before I explain my proposal, I want to highlight also that these > data is represented elsewhere already and it is reused across > different OS's. Thermal data is described using ACPI [3] and > operating systems ACPI-aware do support the interpretation of > thermal data. Linux is one example of such systems (I believe I do > not need to enlist here all systems supporting ACPI). On the other > hand, not all systems have ACPI or are specified to use ACPI. > Thus, here is another reason to represent properly thermal data, so > that we can scale across systems. > > In the specific case of Linux, the common thermal concepts between > ACPI systems and non-ACPI systems have been represented in the > thermal framework (CONFIG_THERMAL). Today, on ACPI systems, thermal > data is fetched from bootloader with help from the common ACPI > parser. For non-ACPI systems, the thermal data is actually coded as > part of device drivers. > > So, to the point, a brief explanation of my proposal goes as > follows: i - trip points: a node to describe a point in the > temperature domain in which the system has to take an action. This > node describes just the point, not the action. Properties here are > temperature, hysteresis, and type (critical, hot, passive, active, > etc). ii - binding parameters: the bind_param node is a node to > describe how actions (cooling devices) get assigned to trip points. > Cooling devices are expected to be loaded in the target system. > Properties here are: cooling device name, weight, trip_mask and > limits. iii - thermal zones: the thermal_zone node is the node > containing all the required info for describing a thermal zone with > hardware thermal limitation, including its bindings with cooling > devices. Properties here are: type, passive_delay, polling_delay, > governor. The thermal_zone node must contain, apart from its own > properties, one node containing trip nodes and one node containing > all the zone bind parameters. > > Here is an example (on OMAP4430): thermal_zone { type = "CPU"; mask > = <0x03>; /* trips writability */ passive_delay = <250>; /* > milliseconds */ polling_delay = <1000>; /* milliseconds */ governor > = "step_wise"; trips { alert@100000{ temperature = <100000>; /* > milliCelsius hysteresis = <2000>; /* milliCelsius */ type = > <THERMAL_TRIP_PASSIVE>; }; crit@125000{ temperature = <125000>; /* > milliCelsius hysteresis = <2000>; /* milliCelsius */ type = > <THERMAL_TRIP_CRITICAL>; }; }; bind_params { action@0{ > cooling_device = "thermal-cpufreq"; weight = <100>; /* percentage > */ mask = <0x01>; /* no limits, using defaults */ }; }; }; > > In this current proposal, a 'thermal_zone' node would be embedded > inside a temperature sensor node, for simplicity. But other > possible builds could embedded them in the device with thermal > limits (CPU nodes, for instance) or they could be not embedded in > any specific node. > > A full documented description can be found here [4]. Also a branch > containing: (a) needed changes in order to have this DT parser; (b) > the DT parser with documentation (c) examples on how drivers could > be changes to use the parser can be found in my branch here [5]. I > wrote the thermal DT parser to build thermal zones with the thermal > framework API. However, if one does not want to do that, it can > simple do not include a CONFIG_THERMAL_OF=y in her/his build, and > the calls will be translated to nops, and the device tree thermal > data can be parsed to somewhere else interested (other subsystem or > even user land). A TODO on this implementation is that it still > lacks the representation of thermal zones composed by several > sensors. However, I believe it is better to take an incremental > approach here. This series can already be used to improve most of > the existing platform thermal drivers (most are CPU thermal > drivers) and to reuse the existing code of some hwmon sensors to > build thermal zones for board thermal requirements. > > I have already posted a patch series with this proposal on [6], > that contains a reference for the original RFC. But looks like my > messages got moderated on device tree mailing list. Obviously, > within PM forum, feedback was quite positive. However, we cannot > proceed without proper assessment of other subsystems. lm-sensors > folks (Guenter) seam to be strongly against this series, as there > is a fear that this may introduce a mis-usage of DT. I still > believe this is needed for hardware description, and thus not a > infringement on DT purposes. > > Please let me know your thoughts on this topic and apologize me if > my previous messages on this topic did not reach you (hope they > reach now). > > All best, > > Eduardo Valentin > > [0] - https://lkml.org/lkml/2013/7/17/621 [1] - > https://lkml.org/lkml/2013/7/18/279 [2] - www.devicetree.org [3] - > http://www.acpi.info/ [4] - > https://git.kernel.org/cgit/linux/kernel/git/evalenti/linux.git/diff/Documentation/devicetree/bindings/thermal/thermal.txt?h=thermal_work/thermal_core/dt_parser&id=405bf0b51457ed055a082af2653d7ce757bc2e91 > > [5] - > https://git.kernel.org/cgit/linux/kernel/git/evalenti/linux.git/log/?h=thermal_work/thermal_core/dt_parser > > [6] - https://lkml.org/lkml/2013/7/17/923 > > _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
