On Wed, Jan 09, 2019 at 08:25:10AM -0600, Rob Herring wrote: > On Wed, Jan 9, 2019 at 8:14 AM Kumar Gala <kumar.gala@xxxxxxxxxx> wrote: > > > > Does anyone know where cell-index came from? If it was ever documented somewhere? > > > > I went looking at some old specs like ePAPR 1.1 and open firmware but couldn’t find it. > > I was trying to find that too as folks love to have indices for their > devices. booting-without-of.txt has some info. It appears it is > supposed to represent an index into some shared resource such as an > offset into some shared register. That hardly scales nor is it what > people want to use it for. > > Here's the part from booting-without-of.txt: It might be worth looking at the old git history of that file, to see if it has anything more specific. > VIII - Specifying Device Power Management Information (sleep property) > =================================================================== > Devices on SOCs often have mechanisms for placing devices into low-power > states that are decoupled from the devices' own register blocks. Sometimes, > this information is more complicated than a cell-index property can > reasonably describe. Thus, each device controlled in such a manner > may contain a "sleep" property which describes these connections. So, what I can recall: * cell-index never came from OF, it was a hack introduced in the pretty early days of flattened trees * I think the primary original purpose was to get consistent ordering on Linux devices (eth0..ethN, sda..sdc, and so forth). That's particularly for devices which have odd out of bounds type control (e.g. ppc 4xx DCRs) so that they can't easily be ordered by register address. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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