linux-kernel - Re: [PATCH v1 2/3] clk: qcom: rcg2: Add support for hardware control mode

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Date:   Tue, 30 Jul 2019 16:20:08 +0530
From:   Taniya Das <tdas@...eaurora.org>
To:     Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/3] clk: qcom: rcg2: Add support for hardware control
 mode

Hello Stephen,

On 7/17/2019 4:48 AM, Stephen Boyd wrote:
> Quoting Taniya Das (2019-07-15 21:19:02)
>> Hello Stephen,
>>
>> Thanks for your review.
>>
>> On 7/16/2019 4:22 AM, Stephen Boyd wrote:
>>> Quoting Taniya Das (2019-05-08 11:24:54)
>>>> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
>>>> index 57dbac9..5bb6d45 100644
>>>> --- a/drivers/clk/qcom/clk-rcg2.c
>>>> +++ b/drivers/clk/qcom/clk-rcg2.c
>>>> @@ -289,6 +289,9 @@ static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
>>>>           cfg |= rcg->parent_map[index].cfg << CFG_SRC_SEL_SHIFT;
>>>>           if (rcg->mnd_width && f->n && (f->m != f->n))
>>>>                   cfg |= CFG_MODE_DUAL_EDGE;
>>>> +       if (rcg->flags & HW_CLK_CTRL_MODE)
>>>> +               cfg |= CFG_HW_CLK_CTRL_MASK;
>>>> +
>>>
>>> Above this we have commit bdc3bbdd40ba ("clk: qcom: Clear hardware clock
>>> control bit of RCG") that clears this bit. Is it possible to always set
>>> this bit and then have an override flag used in sdm845 that says to
>>> _not_ set this bit? Presumably on earlier platforms writing the bit is a
>>> no-op so it's safe to write the bit on those platforms.
>>>
>>> This way, if it's going to be the default we can avoid setting the flag
>>> and only set the flag on older platforms where it shouldn't be done for
>>> some reason.
>>>
>>
>> Not all the subsystem clock controllers might have this hardware control
>> bit set from design. Thus we want to set them based on the flag.
> 
> Yes but what's the percentage of clks that are going to set this flag
> vs. not set this flag? If that is low right now then it's fine but if it
> eventually becomes the standard mechanism it will be easier to opt-out
> of the feature if necessary instead of opt-in.
> 

Currently all the RCGs in GCC need to clear the bit and few RCGs from
the other CCs(DISPCC/VIDEOCC) where the bit is not set from HW requires 
this bit to be set. Thus we want to use this flag mechanism to have the 
flexibility to set.

Once it is a standard we could cleanup to remove this.



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