linux-kernel - Re: [PATCH v3 2/3] clk: qcom: dispcc-sm8650: add missing CLK_SET_RATE

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Message-ID: <CAA8EJpomVKiVrRxSEJmjvNXLGGKVvcr2wGWtE129eUoUfgYC4g@mail.gmail.com>
Date: Wed, 17 Jul 2024 12:49:48 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Konrad Dybcio <konrad.dybcio@...aro.org>
Cc: neil.armstrong@...aro.org, Bjorn Andersson <andersson@...nel.org>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Taniya Das <quic_tdas@...cinc.com>, linux-arm-msm@...r.kernel.org, 
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] clk: qcom: dispcc-sm8650: add missing
 CLK_SET_RATE_PARENT flag

On Wed, 17 Jul 2024 at 12:47, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>
> On 16.07.2024 6:46 PM, Dmitry Baryshkov wrote:
> > On Tue, Jul 16, 2024 at 03:46:24PM GMT, neil.armstrong@...aro.org wrote:
> >> On 16/07/2024 15:44, Dmitry Baryshkov wrote:
> >>> On Tue, 16 Jul 2024 at 15:32, Neil Armstrong <neil.armstrong@...aro.org> wrote:
> >>>>
> >>>> On 16/07/2024 13:20, Dmitry Baryshkov wrote:
> >>>>> On Tue, Jul 16, 2024 at 11:05:22AM GMT, Neil Armstrong wrote:
> >>>>>> Add the missing CLK_SET_RATE_PARENT for the byte0_div_clk_src
> >>>>>> and byte1_div_clk_src, the clock rate should propagate to
> >>>>>> the corresponding _clk_src.
> >>>>>>
> >>>>>> Fixes: 9e939f008338 ("clk: qcom: add the SM8650 Display Clock Controller driver")
> >>>>>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> >>>>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> >>>>>> ---
> >>>>>>    drivers/clk/qcom/dispcc-sm8650.c | 2 ++
> >>>>>>    1 file changed, 2 insertions(+)
> >>>>>
> >>>>> This doesn't seem correct, the byte1_div_clk_src is a divisor, so the
> >>>>> rate should not be propagated. Other platforms don't set this flag.
> >>>>>
> >>>>
> >>>> Why not ? the disp_cc_mdss_byte1_clk_src has CLK_SET_RATE_PARENT and a div_table,
> >>>> and we only pass DISP_CC_MDSS_BYTE1_CLK to the dsi controller.
> >>>
> >>> Yes, the driver sets byte_clk with the proper rate, then it sets
> >>> byte_intf_clk, which results in a proper divisor.
> >>> If we have CLK_SET_RATE_PARENT for byte1_div_clk_src, then setting
> >>> byte_intf_clk rate will also result in a rate change for the byte_clk
> >>> rate.
> >>>
> >>> Note, all other platforms don't set that flag for this reason (I think
> >>> I had to remove it during sm8450 development for this reason).
> >>>
> >>
> >> Ack, I think this deserves a comment explaining this, I'll add it.
> >
> > But where to place it? This applies to _all_ dispcc controllers.
>
> Commit message

It is already committed.

-- 
With best wishes
Dmitry