linux-kernel - Re: [PATCH] clk: samsung: Prevent potential endless loop in the PLL set

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Message-ID: <6736f3d1-31de-6be4-2b1b-50c776025b72@samsung.com>
Date:   Mon, 10 Aug 2020 18:19:14 +0200
From:   Sylwester Nawrocki <s.nawrocki@...sung.com>
To:     Stephen Boyd <sboyd@...nel.org>,
        Tomasz Figa <tomasz.figa@...il.com>
Cc:     COMMON CLK FRAMEWORK <linux-clk@...r.kernel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Mike Turquette <mturquette@...libre.com>,
        SAMSUNG SOC CLOCK DRIVERS <linux-samsung-soc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] clk: samsung: Prevent potential endless loop in the PLL
 set_rate ops

On 07.08.2020 22:20, Stephen Boyd wrote:
> Quoting Sylwester Nawrocki (2020-08-07 10:06:08)

>> On 8/6/20 18:11, Tomasz Figa wrote:
>>>> --- a/drivers/clk/samsung/clk-pll.c
>>>> +++ b/drivers/clk/samsung/clk-pll.c
>>>> @@ -63,6 +63,27 @@ static long samsung_pll_round_rate(struct clk_hw *hw,
>>>>         return rate_table[i - 1].rate;
>>>>  }
>>>>
>>>> +static int samsung_pll_lock_wait(struct samsung_clk_pll *pll,
>>>> +                                unsigned int reg_mask)
>>>> +{
>>>> +       ktime_t timeout;
>>>> +
>>>> +       /* Wait until the PLL is in steady locked state */
>>>> +       timeout = ktime_add_ms(ktime_get(), PLL_TIMEOUT_MS);
>>>> +
>>>> +       while (!(readl_relaxed(pll->con_reg) & reg_mask)) {
>>>> +               if (ktime_after(ktime_get(), timeout)) {
>>>> +                       pr_err("%s: Could not lock PLL %s\n",
>>>> +                               __func__, clk_hw_get_name(&pll->hw));
>>>> +                       return -EFAULT;
>>>> +               }
>>>> +
>>>> +               cpu_relax();
>>>> +       }
>>
>>> Thanks for the patch! Good to have this consolidated. How about going
>>> one step further and using the generic
>>> readl_relaxed_poll_timeout_atomic() helper?
>>
>> Might be a good suggestion, I was considering those helpers but ended
>> up not using them in the patch. The cpu_relax() call might also not be
>> really needed now, when there is the ktime code within the loop.
>> Having multiple occurrences of readl_relaxed_poll_timeout_atomic() could
>> increase the code size due to inlining. How about keeping the 
>> samsung_pll_lock_wait() function and just changing its implementation?
> 
> None of these concerns are mentioned in the commit text. And they seem
> like problems that should be addressed if they're actually problems vs.
> avoiding a common macro and not mentioning them.

Sure, I will improve the commit text, I just didn't investigate in detail
how the common macro could or could not be used before Tomasz's review.