linux-kernel - Re: [PATCH V1 7/9] clk: sprd: add adjustable pll support

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Date:   Thu, 22 Jun 2017 20:06:29 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Stephen Boyd <sboyd@...eaurora.org>,
        Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-clk <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Mark Brown <broonie@...nel.org>,
        Xiaolong Zhang <xiaolong.zhang@...eadtrum.com>,
        Orson Zhai <orson.zhai@...eadtrum.com>,
        Geng Ren <geng.ren@...eadtrum.com>,
        Ben Li <ben.li@...eadtrum.com>
Subject: Re: [PATCH V1 7/9] clk: sprd: add adjustable pll support

Hi Arnd,

On 22 June 2017 at 19:15, Arnd Bergmann <arnd@...db.de> wrote:
> On Thu, Jun 22, 2017 at 12:17 PM, Chunyan Zhang <zhang.lyra@...il.com> wrote:
>> On 20 June 2017 at 09:37, Stephen Boyd <sboyd@...eaurora.org> wrote:
>>> On 06/18, Chunyan Zhang wrote:
>
>>>> +     kint = DIV_ROUND_CLOSEST(((fvco - refin * nint * CCU_PLL_1M)/10000) *
>>>> +     ((mask >> (shift + i)) + 1), refin * 100) << i;
>>>> +     cfg[index].val |= (kint << shift) & mask;
>>>> +     cfg[index].msk |= mask;
>>>> +
>>>> +     ibias_val = pll_get_ibias(fvco, pll->itable);
>>>> +
>>>> +     mask = pmask(pll, PLL_IBIAS);
>>>> +     index = pindex(pll, PLL_IBIAS);
>>>> +     shift = pshift(pll, PLL_IBIAS);
>>>> +     cfg[index].val |= ibias_val << shift & mask;
>>>> +     cfg[index].msk |= mask;
>>>> +
>>>> +     for (i = 0; i < reg_num; i++) {
>>>> +             if (cfg[i].msk)
>>>> +                     ccu_pll_writel(pll, i, cfg[i].val, cfg[i].msk);
>>>> +     }
>>>> +
>>>
>>> Are we waiting for the writel() to go through above? If so we
>>> need a readl() of the same register to make sure the write has
>>> completed before delaying.
>>
>> After writing these configuration registers, we have to wait a certain
>> time to make sure the pll has worked as we configured.  This depends
>> on other circuit part, so we use udelay rather than reading the same
>> register.
>
> I think you have to do both: normally the writel() is not guaranteed
> to arrive at the device until you read back from an address in the
> same device, so the delay must happen after the readl(), or you won't
> know how long to wait for.

I got it, will add the readl() in the next iterator.

Thanks,
Chunyan

>
>        Arnd