On 13/11/13 14:18, Tomasz Figa wrote: > Hi James, Mike, > > On Wednesday 13 of November 2013 14:09:56 James Hogan wrote: >> On 29/05/13 18:39, Mike Turquette wrote: >>> Quoting James Hogan (2013-05-10 05:44:22) >>>> The frequency of some SoC's external oscillators (for example TZ1090's >>>> XTAL1) are configured by the board using pull-ups/pull-downs of >>>> configuration pins, the logic values of which are automatically latched >>>> on reset and available in an SoC register. Add a generic clock component >>>> and DT bindings to handle this. >>>> >>>> It behaves similar to a fixed rate clock (read-only), except it needs >>>> information about a register field (reg, shift, width), and the >>>> clock-frequency is a mapping from register field values to clock >>>> frequencies. >>>> >>> >>> James, >>> >>> Thanks for sending this! It looks mostly good and is a useful clock >>> type to support. Comments below. >> >> Hi Mike, >> >> Sorry for slight delay getting back to you. I had another think about >> this stuff yesterday... >> > > Just a random idea that came to my mind while reading this thread: > > What about modelling this as a set of fixed rate clocks fed into > a read-only mux? Yes, that had occurred to me too. I suppose the arguments against would be: * it doesn't describe the hardware, there is no mux, just a fixed rate clock with a discoverable frequency. * it would sort of work for my small case of only having 9 possible frequencies (although it would be a bit verbose), but wouldn't scale nicely or be extendible to if the frequency was encoded more continuously in the register value. E.g. if the frequency was 1MHz * (the register value - 1) or something crazy like that. Of course that's conjecture and SoC designers probably aren't going to want to use more pins for bootstrap config than necessary. Cheers James -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
