Hi, On Tue, Nov 08, 2011 at 04:39:17PM +0530, R, Durgadoss wrote: > [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. looks like this should be done on hwmon ? -- balbi
Attachment:
signature.asc
Description: Digital signature
