On 08/08/2013 05:10 PM, Dinh Nguyen wrote: > On Thu, 2013-08-08 at 15:13 -0600, Stephen Warren wrote: ... >> Why is there a need to directly represent the divider anywhere? The >> driver can find the rate of the input clock, and I assume it knows what >> rate it wants the clock to run at, so can't it calculate the divider >> based on those two pieces of information? > > CC: Chris Ball >> >> Or, does the driver really not know what rate it wants the clock to be >> after the internal divider? If not, then I think that *rate* should be >> recorded in DT, not the divider to obtain that rate. >> > > I believe that this is the case, that the driver does not know what rate > it will clock the SD card at. I think internally we did have a "bus_hz" > in DT a while back. I guess I don't really understand why it would be > better to have a *rate* DT entry instead of a fixed-divider entry? The value of the divider depends on two things: 1) Input clock rate. 2) Desired rate after applying the internal divider. The input clock rate may vary, either between SoCs the IP is integrated into, or even at run-time perhaps base on clk_set_rate() etc. If the MMC driver knows the clock rate it wants to run at, it can calculate the divider easily; it can automatically adjust to any input clock that its environment may provide. If the MMC driver is simply told "use this divider", that's encoding assumptions about the rate of the input clock which might not be valid;. Encoding the desire clock rate within the MMC HW block allows the divider to be calculated based on the actual environment. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
