linux-kernel - Re: [PATCH 1/2] clk: zynqmp: pll: add set_pll_mode to check condition in zynqmp_pll

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Date:   Tue, 30 Mar 2021 20:18:03 +0800
From:   "quanyang.wang" <quanyang.wang@...driver.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Michal Simek <michal.simek@...inx.com>,
        Rajan Vaja <rajan.vaja@...inx.com>,
        Jolly Shah <jolly.shah@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Rohit Visavalia <RVISAVAL@...inx.com>
Subject: Re: [PATCH 1/2] clk: zynqmp: pll: add set_pll_mode to check condition
 in zynqmp_pll_enable

Hi Laurent,

On 3/21/21 8:01 AM, Laurent Pinchart wrote:
> Hi Quanyang,
>
> Thank you for the patch.
>
> On Fri, Mar 19, 2021 at 06:07:17PM +0800, quanyang.wang@...driver.com wrote:
>> From: Quanyang Wang <quanyang.wang@...driver.com>
>>
>> If there is a IOCTL_SET_PLL_FRAC_MODE request sent to ATF ever,
>> we shouldn't skip invoking PM_CLOCK_ENABLE fn even though this
>> pll has been enabled. In ATF implementation, it will only assign
>> the mode to the variable (struct pm_pll *)pll->mode when handling
>> IOCTL_SET_PLL_FRAC_MODE call. Invoking PM_CLOCK_ENABLE can force
>> ATF send request to PWU to set the pll mode to PLL's register.
>>
>> There is a scenario that happens in enabling VPLL_INT(clk_id:96):
>> 1) VPLL_INT has been enabled during booting.
>> 2) A driver calls clk_set_rate and according to the rate, the VPLL_INT
>>     should be set to FRAC mode. Then zynqmp_pll_set_mode is called
>>     to pass IOCTL_SET_PLL_FRAC_MODE to ATF. Note that at this point
>>     ATF just stores the mode to a variable.
>> 3) This driver calls clk_prepare_enable and zynqmp_pll_enable is
>>     called to try to enable VPLL_INT pll. Because of 1), the function
>>     zynqmp_pll_enable just returns without doing anything after checking
>>     that this pll has been enabled.
>>
>> In the scenario above, the pll mode of VPLL_INT will never be set
>> successfully. So adding set_pll_mode to chec condition to fix it.
> s/chec/check/
>
>> Signed-off-by: Quanyang Wang <quanyang.wang@...driver.com>
>> ---
>>   drivers/clk/zynqmp/pll.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/clk/zynqmp/pll.c b/drivers/clk/zynqmp/pll.c
>> index 92f449ed38e5..f1e8f37d7f52 100644
>> --- a/drivers/clk/zynqmp/pll.c
>> +++ b/drivers/clk/zynqmp/pll.c
>> @@ -14,10 +14,12 @@
>>    * struct zynqmp_pll - PLL clock
>>    * @hw:		Handle between common and hardware-specific interfaces
>>    * @clk_id:	PLL clock ID
>> + * @set_pll_mode:	Whether an IOCTL_SET_PLL_FRAC_MODE request be sent to ATF
>>    */
>>   struct zynqmp_pll {
>>   	struct clk_hw hw;
>>   	u32 clk_id;
>> +	bool set_pll_mode;
>>   };
>>   
>>   #define to_zynqmp_pll(_hw)	container_of(_hw, struct zynqmp_pll, hw)
>> @@ -81,6 +83,8 @@ static inline void zynqmp_pll_set_mode(struct clk_hw *hw, bool on)
>>   	if (ret)
>>   		pr_warn_once("%s() PLL set frac mode failed for %s, ret = %d\n",
>>   			     __func__, clk_name, ret);
>> +	else
>> +		clk->set_pll_mode = true;
>>   }
>>   
>>   /**
>> @@ -240,9 +244,14 @@ static int zynqmp_pll_enable(struct clk_hw *hw)
>>   	u32 clk_id = clk->clk_id;
>>   	int ret;
>>   
>> -	if (zynqmp_pll_is_enabled(hw))
>> +	/* Don't skip enabling clock if there is an IOCTL_SET_PLL_FRAC_MODE request
>> +	 * that has been sent to ATF.
>> +	 */
> Very small issue, multiline kerneldoc comments are supposed to start
> with a '/*' on its own line:
>
> 	/*
> 	 * Don't skip enabling clock if there is an IOCTL_SET_PLL_FRAC_MODE
> 	 * request that has been sent to ATF.
> 	 */
>
>> +	if (zynqmp_pll_is_enabled(hw) && (!clk->set_pll_mode))
>>   		return 0;
>>   
>> +	clk->set_pll_mode = false;
>> +
>>   	ret = zynqmp_pm_clock_enable(clk_id);
>>   	if (ret)
>>   		pr_warn_once("%s() clock enable failed for %s, ret = %d\n",
> This fixes the DPSUB clock issue, so
>
> Tested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>
> I however wonder if this is the best solution. Shouldn't we instead fix
> it on the ATF side, to program the hardware when zynqmp_pll_set_mode()
> is called if the clock is already enabled ?
>
> Just reading the code, I can immediately see another potential issue in
> zynqmp_pll_set_mode(). The function is called from
> zynqmp_pll_round_rate(), which seems completely wrong, as
> zynqmp_pll_round_rate() is supposed to only perform rate calculation,
> not program the hardware. Am I missing something, or does the PLL
> implementation need to be reworked more extensively than this ?

I will send another patch to fix this issue.

Thanks,

Quanyang

>