[PATCH] clk: sunxi: Accept a greater rate when setting a parent clock

[Jean-Francois Moine]

On Tue, 29 Mar 2016 11:38:27 +0200
Maxime Ripard <maxime.ripard at free-electrons.com> wrote:

> Hi,
> 
> On Mon, Mar 21, 2016 at 09:25:49AM +0100, Jean-Francois Moine wrote:
> > On Mon, 21 Mar 2016 08:25:46 +0100
> > Maxime Ripard <maxime.ripard at free-electrons.com> wrote:
> > 
> > > > -	/* find the parent that can help provide the fastest rate <= rate */
> > > > +	/* find the parent that can help provide the fastest rate */
> > > >  	num_parents = clk_hw_get_num_parents(hw);
> > > >  	for (i = 0; i < num_parents; i++) {
> > > >  		parent = clk_hw_get_parent_by_index(hw, i);
> > > > @@ -100,7 +100,7 @@ static int clk_factors_determine_rate(struct clk_hw *hw,
> > > >  		child_rate = clk_factors_round_rate(hw, req->rate,
> > > >  						    &parent_rate);
> > > >  
> > > > -		if (child_rate <= req->rate && child_rate > best_child_rate) {
> > > > +		if (child_rate > best_child_rate) {
> > > 
> > > I'm not sure this would work, since you'll end up picking the fastest
> > > rate without considering whether it is the closest or not.
> > > 
> > > I guess what you want here is using the absolute difference between
> > > the requested rate and the rate you're evaluating.
> > > 
> > > That being said, we had a similar discussion for SPI around a month
> > > ago where we wanted a rate strictly lower than the requested one. I
> > > guess it's time to add a flag to tell how you want to round.
> > 
> > You are right, I just removed half of the constraint, but I still wonder
> > why does this sequence introduced by the commit 862b728387aef3a37
> > (clk: sunxi: factors: automatic reparenting support) do
> > 	"provide the fastest rate <= rate"
> > instead of
> > 	"provide the closest rate" ?
> 
> I guess it's a confusing wording, in this case where you try to have
> the closest rate but below the requested rate, what you want is
> actually the fastest rate that doesn't trip above the requested rate,
> hence the comment I guess.

This does not answer my question.

What I want to know is: will everyone be OK if I change the actual test
to "provide the closest rate"?

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Jef		|		http://moinejf.free.fr/