From: emilio@elopez•com.ar (Emilio López)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] clk: sunxi: Accept a greater rate when setting a parent clock
Date: Wed, 30 Mar 2016 17:49:47 -0300 [thread overview]
Message-ID: <56FC3BEB.8030106@elopez.com.ar> (raw)
In-Reply-To: <20160321092549.4e6245e4f02839e29aeb86a9@free.fr>
[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 <maxime.ripard@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" ?
>
> 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
next prev parent reply other threads:[~2016-03-30 20:49 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20160310081658.B749246B@mail.free-electrons.com>
2016-03-21 7:25 ` [PATCH] clk: sunxi: Accept a greater rate when setting a parent clock Maxime Ripard
2016-03-21 8:25 ` Jean-Francois Moine
2016-03-29 9:38 ` Maxime Ripard
2016-03-29 10:08 ` Jean-Francois Moine
2016-03-30 20:49 ` Emilio López [this message]
2016-04-14 17:24 ` Maxime Ripard
2016-04-14 18:14 ` Jean-Francois Moine
2016-04-14 19:31 ` Maxime Ripard
[not found] <E1advmk-0004Nt-Ba@bombadil.infradead.org>
2016-03-18 7:47 ` Jean-Francois Moine
2016-03-10 7:15 Jean-Francois Moine
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