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

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Date:   Fri, 7 Aug 2020 19:06:08 +0200
From:   Sylwester Nawrocki <s.nawrocki@...sung.com>
To:     Tomasz Figa <tomasz.figa@...il.com>
Cc:     "open list:COMMON CLK FRAMEWORK" <linux-clk@...r.kernel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Mike Turquette <mturquette@...libre.com>,
        "moderated list: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

Hi Tomasz,

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?

-- 
Thanks,
Sylwester