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

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Message-ID: <278354ec-532b-48de-8ee1-5477ddb4a285@linaro.org>
Date: Tue, 16 Jul 2024 15:46:24 +0200
From: neil.armstrong@...aro.org
To: Dmitry Baryshkov <dmitry.baryshkov@...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 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.

Thanks,
Neil