Hi All, [Very Sorry for the Big Email] [I have posted this on lm-sensors and platform-drivers-x86 lists earlier. As per some recommendations there, posting it here] As we all know, Linux is increasingly being used in handhelds. The Hardware that supports the handhelds is also becoming Performance-centric. With this, we need a way to efficiently monitor the current consumption of the platform and take actions when the platform draws more current, than it should. Where this can happen ? ----------------------- In a handheld, there are many components that demand high Current. For example, Camera Flash, Video Streaming, 3G Voice Call etc. Typically, two or more of these components are used simultaneously in a real-time scenario. When this happens, the current draw of the platform surges. If this surge lasts for more than a specific time, it could crash the platform irrecoverably. How do we tackle this ? ----------------------- In Intel Medfield (Atom based) platform we had a driver that Configures the current limits. When the platform current draws more current than the programmed limit, the hardware generates interrupt. The driver receives this interrupt and notifies the user space to take appropriate actions. The patch and the subsequent discussions can be found here: http://comments.gmane.org/gmane.linux.drivers.platform.x86.devel/1197 To Generalize: -------------- With many more platforms to come, having a separate driver for each results in heavy code duplication. Also, there arises a problem of where to put these kind of drivers ? Hence I propose the idea of having a Current Management subsystem. This will provide a generic ABI, API, so that the platform specific drivers can register with this framework (and thus avail the basic needs) and handle the events in their own way. In simple terms, this framework will offer something like this: Current[1-N]_limit - set of current limits Voltage[1-X]_limit - set of voltage limits Controllers[1-Y]_enable - These are the components by throttling/ disabling which the current consumption can be brought down. With the Controllers we can follow two approaches: A) Each component driver registers with the current framework and gets notified when the current surge happens. On receiving the notification, it throttles its performance. There will be a follow-up notification, indicating that 'we are out of the high current' situation; so that the component resumes to operation at its full performance. B) The Current framework forwards the notification to the upper layers and lets them decide what to do. I agree that A) bloats the size of all the component drivers a bit, but considering the fact that the surge has to be brought down as soon as possible (and the delay in reacting to the event if we pass it to the upper layers) I am inclined towards A). I would like to see the opinion of the community on this entire stuff, before I start writing some code. Please Help, Durga -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
