linux-kernel - Re: [PATCH V3 06/17] clk: tegra: pll: save and restore pll context

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Date:   Tue, 25 Jun 2019 14:22:43 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Stephen Boyd <sboyd@...nel.org>, <jason@...edaemon.net>,
        <jonathanh@...dia.com>, <linus.walleij@...aro.org>,
        <marc.zyngier@....com>, <mark.rutland@....com>, <stefan@...er.ch>,
        <tglx@...utronix.de>, <thierry.reding@...il.com>
CC:     <pdeschrijver@...dia.com>, <pgaikwad@...dia.com>,
        <linux-clk@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
        <jckuo@...dia.com>, <josephl@...dia.com>, <talho@...dia.com>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <mperttunen@...dia.com>, <spatra@...dia.com>, <robh+dt@...nel.org>,
        <digetx@...il.com>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH V3 06/17] clk: tegra: pll: save and restore pll context


On 6/25/19 1:46 PM, Stephen Boyd wrote:
> Quoting Sowjanya Komatineni (2019-06-18 00:46:20)
>> diff --git a/drivers/clk/tegra/clk-pll.c b/drivers/clk/tegra/clk-pll.c
>> index 1583f5fc992f..4b0ed8fc6268 100644
>> --- a/drivers/clk/tegra/clk-pll.c
>> +++ b/drivers/clk/tegra/clk-pll.c
>> @@ -1008,6 +1008,54 @@ static unsigned long clk_plle_recalc_rate(struct clk_hw *hw,
>>          return rate;
>>   }
>>   
>> +void tegra_clk_sync_state_pll(struct clk_hw *hw)
>> +{
>> +       if (!__clk_get_enable_count(hw->clk))
>> +               clk_pll_disable(hw);
>> +       else
>> +               clk_pll_enable(hw);
>> +}
>> +
>> +static int tegra_clk_pll_save_context(struct clk_hw *hw)
>> +{
>> +       struct tegra_clk_pll *pll = to_clk_pll(hw);
>> +
>> +       pll->rate = clk_hw_get_rate(hw);
>> +
>> +       if (!strcmp(__clk_get_name(hw->clk), "pll_mb"))
>> +               pll->pllbase_ctx = pll_readl_base(pll);
>> +       else if (!strcmp(__clk_get_name(hw->clk), "pll_re_vco"))
>> +               pll->pllbase_ctx = pll_readl_base(pll) & (0xf << 16);
>> +
>> +       return 0;
>> +}
>> +
>> +static void tegra_clk_pll_restore_context(struct clk_hw *hw)
>> +{
>> +       struct tegra_clk_pll *pll = to_clk_pll(hw);
>> +       u32 val;
>> +
>> +       if (clk_pll_is_enabled(hw))
>> +               return;
>> +
>> +       if (!strcmp(__clk_get_name(hw->clk), "pll_mb")) {
> Is there any way to avoid doing a string comparison here, and instead do
> something like a pointer comparison? Or maybe look at some flag in the
> tegra_clk_pll to figure out what to do differently? Using a string
> comparison is not too nice. Or even have different clk ops for the
> different clks and then do different things in this restore clk_op?
OK, Will update...
>> +               pll_writel_base(pll->pllbase_ctx, pll);
>> +       } else if (!strcmp(__clk_get_name(hw->clk), "pll_re_vco")) {
>> +               val = pll_readl_base(pll);
>> +               val &= ~(0xf << 16);
>> +               pll_writel_base(pll->pllbase_ctx | val, pll);
>> +       }
>> +
>> +       if (pll->params->set_defaults)
>> +               pll->params->set_defaults(pll);
>> +
>> +       clk_set_rate(hw->clk, pll->rate);
> Do you need to call clk_set_rate() here to change the frequency of the
> clk or just the parents of the clk, or both? I'd think that when we're
> restoring the clk the cached rate of the clk would match whatever we're
> restoring to, so this is a NOP. So does this do anything?
>
> I'd prefer that the restore ops just restore the clk hardware state of
> the clk_hw passed in, and not try to fix up the entire tree around a
> certain clk, if that's even possible.

On restore, need to program tegra plls rate back to the same rate as 
they were before suspend, so I am calling clk_set_rate to program pll 
m,n,p values in hw registers.

>> +
>> +       /* do not sync pllx state here. pllx is sync'd after dfll resume */
>> +       if (strcmp(__clk_get_name(hw->clk), "pll_x"))
>> +               tegra_clk_sync_state_pll(hw);
>> +}
>> +
>>   const struct clk_ops tegra_clk_pll_ops = {
>>          .is_enabled = clk_pll_is_enabled,
>>          .enable = clk_pll_enable,
>> @@ -1015,6 +1063,8 @@ const struct clk_ops tegra_clk_pll_ops = {
>>          .recalc_rate = clk_pll_recalc_rate,
>>          .round_rate = clk_pll_round_rate,
>>          .set_rate = clk_pll_set_rate,
>> +       .save_context = tegra_clk_pll_save_context,
>> +       .restore_context = tegra_clk_pll_restore_context,