linux-kernel - Re: [PATCH v6] clk: qcom: Add lpass clock controller driver for SDM845

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Date:   Wed, 10 Oct 2018 11:42:27 +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 v6] clk: qcom: Add lpass clock controller driver for
 SDM845



On 10/10/2018 2:22 AM, Stephen Boyd wrote:
> Quoting Taniya Das (2018-10-09 10:26:38)
>> Hello Stephen,
>>
>> On 10/8/2018 8:14 AM, Stephen Boyd wrote:
>>> Quoting Taniya Das (2018-10-04 05:02:26)
>>>> Add support for the lpass clock controller found on SDM845 based devices.
>>>> This would allow lpass peripheral loader drivers to control the clocks to
>>>> bring the subsystem out of reset.
>>>> LPASS clocks present on the global clock controller would be registered
>>>> with the clock framework based on the device tree flag. Also do not gate
>>>> these clocks if they are left unused.
>>>
>>> Why not gate them? This statement states what the code is doing, not why
>>> it's doing it which is the more crucial information that should be
>>> described in the commit text. Also, please add a comment about it to the
>>> code next to the flag.
>>>
>>> I am concerned that it doesn't make any sense though, so probably it
>>> shouldn't be marked as CLK_IGNORE_UNUSED and it's papering over some
>>> other larger bug that needs to be fixed.
>>>
>>
>> It does not have any bug, it is just that to access these lpass
>> registers we would need the GCC lpass registers to be enabled. I would
>> update the same in the commit text.
>>
>> During clock late_init these clocks should not be accessed to check the
>> clock status as they would result in unclocked access. The client would
>> request these clocks in the correct order and it would not have any issue.
>>
> 
> That seems like the bug right there. If the LPASS registers can't be
> accessed unless the clks in GCC are enabled then this driver needs to
> turn the clks on before reading/writing registers. Marking the clks as
> ignore unused is skipping around the real problem.
> 

If the driver requests for the clocks they would maintain the order. But 
if the clock late init call is invoked before the driver requests, there 
is no way I could manage this dependency, that is the only reason to 
mark them unused.

>>
>>>>
>>>> Signed-off-by: Taniya Das <tdas@...eaurora.org>
>>>> ---
>>>> diff --git a/drivers/clk/qcom/gcc-sdm845.c b/drivers/clk/qcom/gcc-sdm845.c
>>>> index 08d593e..6379b8b 100644
>>>> --- a/drivers/clk/qcom/gcc-sdm845.c
>>>> +++ b/drivers/clk/qcom/gcc-sdm845.c
>>>> @@ -3583,6 +3611,13 @@ static int gcc_sdm845_probe(struct platform_device *pdev)
>>>>           if (ret)
>>>>                   return ret;
>>>>
>>>> +       if (!of_property_read_bool(pdev->dev.of_node, "qcom,lpass-protected")) {
>>>> +               gcc_sdm845_clocks[GCC_LPASS_Q6_AXI_CLK] =
>>>> +                       &gcc_lpass_q6_axi_clk.clkr;
>>>> +               gcc_sdm845_clocks[GCC_LPASS_SWAY_CLK] =
>>>> +                       &gcc_lpass_sway_clk.clkr;
> 
> For all intents and purposes could we not just mark these two as
> CLK_IS_CRITICAL and then let the LPASS turn these on and off when it
> cares (does it ever do so)? Or even just turn them on once in probe here
> with direct register writes and then not care anymore to touch them
> again? Or do we need to turn these clks on again later on when the
> subsystem crashes to read/write the registers and cycle the clks back on
> and off?
> 
>>>> +       }
>>>> +
>>>>           return qcom_cc_really_probe(pdev, &gcc_sdm845_desc, regmap);
>>>>    }
>>>>
>>>> diff --git a/drivers/clk/qcom/lpasscc-sdm845.c b/drivers/clk/qcom/lpasscc-sdm845.c
>>>> new file mode 100644
>>>> index 0000000..f7b9b0f
>>>> --- /dev/null
>>>> +++ b/drivers/clk/qcom/lpasscc-sdm845.c
>>>> +               },
>>>> +       },
>>>> +};
>>>> +
>>>> +static int lpass_clocks_sdm845_probe(struct platform_device *pdev, int index,
>>>> +                                    const struct qcom_cc_desc *desc)
>>>> +{
>>>> +       struct regmap *regmap;
>>>> +       struct resource *res;
>>>> +       void __iomem *base;
>>>> +
>>>> +       res = platform_get_resource(pdev, IORESOURCE_MEM, index);
>>>> +       base = devm_ioremap_resource(&pdev->dev, res);
>>>> +       if (IS_ERR(base))
>>>> +               return PTR_ERR(base);
>>>> +
>>>> +       regmap = devm_regmap_init_mmio(&pdev->dev, base, desc->config);
>>>> +       if (IS_ERR(regmap))
>>>> +               return PTR_ERR(regmap);
>>>
>>> If this happens again in the future we should move this into the
>>> common.c file and let qcom_cc_probe_index() exist.
>>>
>>
>> Yes, I agree, could submit a patch to add the new function and then
>> clean it up.
> 
> Ok, but please don't do anything now because we don't care yet.
> 

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