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Message-ID: <64749bf4.5d0a0220.325c0.64b5@mx.google.com>
Date: Mon, 29 May 2023 14:34:57 +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 Mon, May 29, 2023 at 02:12:23PM +0200, Konrad Dybcio wrote:
>
>
> On 28.05.2023 14:37, Christian Marangi wrote:
> > 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?
> Yeah that would be more readable!
>
> >
> >>> + 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.
> Hm.. I'm not sure what's the expected behavior here.. Stephen?
>
I have this implementation rady, if you want I can send this revision
and discuss that in v5 directly. It's WARN and returning -EINVAL.
> >
> >>> +
> >>> + 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.
> >
--
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