linux-kernel - Re: [PATCH v4 2/3] clk: qcom: clk-rcg2: add support for rcg2 freq multi ops

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Date:   Sun, 28 May 2023 14:37:26 +0200
From:   Christian Marangi <ansuelsmth@...il.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] clk: qcom: clk-rcg2: add support for rcg2 freq
 multi ops

On Sat, May 27, 2023 at 06:11:16PM +0200, Konrad Dybcio wrote:
> 
> 
> On 27.04.2023 17:07, Christian Marangi wrote:
> > Some RCG frequency can be reached by multiple configuration.
> > 
> > Add clk_rcg2_fm_ops ops to support these special RCG configurations.
> > 
> > These alternative ops will select the frequency using a CEIL policy.
> > 
> > When the correct frequency is found, the correct config is selected by
> > calculating the final rate (by checking the defined parent and values
> > in the config that is being checked) and deciding based on the one that
> > is less different than the requested one.
> > 
> > These check are skipped if there is just on config for the requested
> > freq.
> > 
> > qcom_find_freq_multi is added to search the freq with the new struct
> > freq_multi_tbl.
> > __clk_rcg2_select_conf is used to select the correct conf by simulating
> > the final clock.
> > 
> > Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> > ---
> >  drivers/clk/qcom/clk-rcg.h  |   1 +
> >  drivers/clk/qcom/clk-rcg2.c | 152 ++++++++++++++++++++++++++++++++++++
> >  drivers/clk/qcom/common.c   |  18 +++++
> >  drivers/clk/qcom/common.h   |   2 +
> >  4 files changed, 173 insertions(+)
> > 
> > diff --git a/drivers/clk/qcom/clk-rcg.h b/drivers/clk/qcom/clk-rcg.h
> > index dc85b46b0d79..f8ec989ed3d9 100644
> > --- a/drivers/clk/qcom/clk-rcg.h
> > +++ b/drivers/clk/qcom/clk-rcg.h
> > @@ -188,6 +188,7 @@ struct clk_rcg2_gfx3d {
> >  
> >  extern const struct clk_ops clk_rcg2_ops;
> >  extern const struct clk_ops clk_rcg2_floor_ops;
> > +extern const struct clk_ops clk_rcg2_fm_ops;
> >  extern const struct clk_ops clk_rcg2_mux_closest_ops;
> >  extern const struct clk_ops clk_edp_pixel_ops;
> >  extern const struct clk_ops clk_byte_ops;
> > diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> > index 76551534f10d..4f2fe012ef5f 100644
> > --- a/drivers/clk/qcom/clk-rcg2.c
> > +++ b/drivers/clk/qcom/clk-rcg2.c
> > @@ -266,6 +266,104 @@ static int _freq_tbl_determine_rate(struct clk_hw *hw, const struct freq_tbl *f,
> >  	return 0;
> >  }
> >  
> > +static const struct freq_conf *
> > +__clk_rcg2_select_conf(struct clk_hw *hw, const struct freq_multi_tbl *f,
> > +		       unsigned long req_rate)
> > +{
> > +	unsigned long best_rate = 0, parent_rate, rate;
> > +	const struct freq_conf *conf, *best_conf;
> > +	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> > +	struct clk_hw *p;
> > +	int index, i;
> > +
> > +	/* Exit early if only one config is defined */
> > +	if (f->num_confs == 1)
> > +		return f->confs;
> > +
> > +	/* Search in each provided config the one that is near the wanted rate */
> > +	for (i = 0, conf = f->confs; i < f->num_confs; i++, conf++) {
> > +		index = qcom_find_src_index(hw, rcg->parent_map, conf->src);
> > +		if (index < 0)
> > +			continue;
> > +
> > +		p = clk_hw_get_parent_by_index(hw, index);
> > +		if (!p)
> > +			continue;
> > +
> > +		parent_rate =  clk_hw_get_rate(p);
> > +		rate = calc_rate(parent_rate, conf->n, conf->m, conf->n, conf->pre_div);
> > +
> > +		if (rate == req_rate) {
> > +			best_conf = conf;
> > +			break;
> > +		}
> > +
> > +		if (abs(req_rate - rate) < abs(best_rate - rate)) {
> Shouldn't this be:
> 
> if (abs(req_rate - rate) < abs(best_rate - req_rate)
> 
> ?
> 
> this way it'd say
> 
> "if this iteration's rate is closer to the requested one than the
> best one we've found yet, it's better"
>

Hi, thanks for the review!

I wonder if even better would be something where we save the best rate
diff and just compare that.

rate_diff = abs(req_rate - rate)
if (rate_diff < best_rate_diff) {
	best_rate_diff = rate_diff;
	best_conf = conf;
}

And best_rate_diff init to ULONG_MAX?

> > +			best_rate = rate;
> > +			best_conf = conf;
> > +		}
> > +	}
> > +
> > +	/*
> > +	 * Very unlikely.
> > +	 * Force the first conf if we can't find a correct config.
> > +	 */
> > +	if (unlikely(i == f->num_confs))
> > +		best_conf = f->confs;
> Is that a supported scenario or would it be a device driver / clock
> driver error?
> 

It's to handle case for the 2 continue in the loop and arriving in a
situation where best_conf was never set?

Should we return a warning and an ERR_PTR? Idea was to provide a best
effort selection.

> > +
> > +	return best_conf;
> > +}
> > +
> > +static int _freq_tbl_fm_determine_rate(struct clk_hw *hw, const struct freq_multi_tbl *f,
> > +				       struct clk_rate_request *req)
> > +{
> > +	unsigned long clk_flags, rate = req->rate;
> > +	const struct freq_conf *conf;
> > +	struct clk_hw *p;
> > +	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> swap lines 2, 3, 4 to 4, 2, 3 and you'll get a revers-Christmas-tree!
> 

Thanks, didn't notice this. Will do in v5.

-- 
	Ansuel