linux-kernel - Re: [PATCH 06/14] clk: qcom: clk-branch: Add support for BRANCH_HALT

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Message-ID: <dfafb945-69f7-4378-9bb0-72eee37de235@quicinc.com>
Date: Fri, 18 Oct 2024 16:32:47 +0530
From: Taniya Das <quic_tdas@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Stephen Boyd
	<sboyd@...nel.org>
CC: Bjorn Andersson <andersson@...nel.org>,
        Conor Dooley
	<conor+dt@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        "Krzysztof
 Kozlowski" <krzk+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Philipp Zabel
	<p.zabel@...gutronix.de>, Rob Herring <robh@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Kalpak Kawadkar
	<quic_kkawadka@...cinc.com>
Subject: Re: [PATCH 06/14] clk: qcom: clk-branch: Add support for
 BRANCH_HALT_POLL flag



On 10/18/2024 3:35 AM, Dmitry Baryshkov wrote:
> On Thu, Oct 17, 2024 at 11:03:20AM -0700, Stephen Boyd wrote:
>> Quoting Dmitry Baryshkov (2024-10-17 09:56:56)
>>> From: Kalpak Kawadkar <quic_kkawadka@...cinc.com>
>>>
>>> On some platforms branch clock will be enabled before Linux.
>>> It is expectated from the clock provider is to poll on the clock
>>
>> Unfortunately 'expectated' is not a word. The sentence is also
>> grammatically incorrect.
>>
>>> to ensure it is indeed enabled and not HW gated, thus add
>>> the BRANCH_HALT_POLL flag.
>> [...]
>>> diff --git a/drivers/clk/qcom/clk-branch.c b/drivers/clk/qcom/clk-branch.c
>>> index 229480c5b075a0e70dc05b1cb15b88d29fd475ce..c4c7bd565cc9a3926e24bb12ed6355ec6ddd19fb 100644
>>> --- a/drivers/clk/qcom/clk-branch.c
>>> +++ b/drivers/clk/qcom/clk-branch.c
>>> @@ -76,6 +76,7 @@ static int clk_branch_wait(const struct clk_branch *br, bool enabling,
>>>                  udelay(10);
>>>          } else if (br->halt_check == BRANCH_HALT_ENABLE ||
>>>                     br->halt_check == BRANCH_HALT ||
>>> +                  br->halt_check == BRANCH_HALT_POLL ||
>>
>> The name is confusing. The halt check is already "polling", i.e. this
>> isn't a different type of halt check. This is really something like
>> another branch flag that doesn't have to do with the halt checking and
>> only to do with skipping writing the enable bit. Maybe we should
>> introduce another clk_ops for these types of clks instead.
> 
> SGTM. All clocks with this flag use clk_branch2_aon_ops, so it is easy
> to switch to a separate clk_ops.
> 

The basic requirement here is to just poll in both enable/disable, but 
HLOS cannot update the CLK_ENABLE bit. The clock could be gated by the 
bandwidth vote and thus to ensure the clock is in good state before the 
consumers start using the subsystem.

We can definitely think for a different ops, I think it is better we 
have a good name to the flag.

>>
>>>                     (enabling && voted)) {
>>>                  int count = 200;
>>>   
>>> @@ -97,6 +98,10 @@ static int clk_branch_toggle(struct clk_hw *hw, bool en,
>>>          struct clk_branch *br = to_clk_branch(hw);
>>>          int ret;
>>>   
>>> +       if (br->halt_check == BRANCH_HALT_POLL) {
>>
>> Remove braces
>>
>>> +               return  clk_branch_wait(br, en, check_halt);
>>
>> Remove extra space      ^
>>
>>> +       }
>>> +
> 

-- 
Thanks & Regards,
Taniya Das.