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

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Message-ID: <CAA8EJpr9L+AKDhuHfQa=Nco7fvG9vLH3a+gxVhENrhz12b3n=Q@mail.gmail.com>
Date: Tue, 16 Jul 2024 16:44:34 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: neil.armstrong@...aro.org
Cc: Bjorn Andersson <andersson@...nel.org>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.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 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).

-- 
With best wishes
Dmitry