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

From: [email-masked] (Emilio López)
Date: Wed, 30 Mar 2016 17:49:47 -0300

[Sorry for the delay, I meant to reply to this post a while back but I
forgot]

El 21/03/16 a las 05:25, Jean-Francois Moine escribi?:
> On Mon, 21 Mar 2016 08:25:46 +0100
> Maxime Ripard <[email-masked]> 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" ?
> 
> Emilio?

Overclocking components is usually not a good default in my opinion. I
don't recall at the moment if there was some other justification apart
from playing it safe.

Cheers,
Emilio