Remi Pommarel <r...@triplefau.lt> writes: > Some bcm2835 clocks used by hardware (like "PWM" or "H264") can have multiple > parents. These clocks divide the rate of one parent which can be selected by > setting the proper bits in their clock control register. > > Previously all these parents where handled by a mux clock. But a mux clock > cannot be used because updating clock control register to select parent needs > a > password to be xor'd with the parent index.
Good point. I previously was doing parent detection from muxes manually, then simplified to using the generic mux later. I didn't have any clocks I wanted to change mux on, so I missed this requirement. It looks like there's not too much work to folding the muxing back into the driver, so it seems like you have a good plan. > -static long bcm2835_clock_round_rate(struct clk_hw *hw, > - unsigned long rate, > - unsigned long *parent_rate) > -{ > - struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw); > - u32 div = bcm2835_clock_choose_div(hw, rate, *parent_rate); > - > - return bcm2835_clock_rate_from_divisor(clock, *parent_rate, div); > -} > - > static unsigned long bcm2835_clock_get_rate(struct clk_hw *hw, > unsigned long parent_rate) > { > @@ -1278,13 +1268,69 @@ static int bcm2835_clock_set_rate(struct clk_hw *hw, > return 0; > } > > +static int bcm2835_clock_determine_source(struct clk_hw *hw, > + struct clk_rate_request *req) > +{ > + struct clk_hw *parent, *best_parent = NULL; > + struct clk_rate_request parent_req; > + unsigned long prate, best_rate = ULONG_MAX; > + size_t i; > + > + /* > + * Select parent clock that has the closest but higher rate > + */ > + for (i = 0; i < clk_hw_get_num_parents(hw); ++i) { > + parent = clk_hw_get_parent_by_index(hw, i); > + if (!parent) > + continue; > + parent_req = *req; > + prate = clk_hw_get_rate(parent); > + if (prate < best_rate && prate >= req->rate) { > + best_parent = parent; > + best_rate = prate; > + } > + } > + > + if (!best_parent) > + return -EINVAL; > + > + req->best_parent_hw = best_parent; > + req->best_parent_rate = best_rate; > + > + return 0; > +} It looks like you've dropped the use of the divisor off of the PLL channel when setting a rate. That seems bad for all the other clocks in the system, and a feature we couldn't lose. Also, you're choosing the lowest but higher rate, while mux_is_better_rate() chooses the highest but lower rate (which seems much safer). What led to that choice? Also, if we're going to have this function, I think it should be called "bcm2835_clock_determine_rate" to match the method name. The parent get/setting looks good, though.
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