linux-kernel - Re: [PATCH v8 08/13] drivers: memory: add DMC driver for Exynos5422

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Date:   Thu, 6 Jun 2019 13:45:15 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Lukasz Luba <l.luba@...tner.samsung.com>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        Bartłomiej Żołnierkiewicz 
        <b.zolnierkie@...sung.com>, kgene@...nel.org,
        Chanwoo Choi <cw00.choi@...sung.com>,
        kyungmin.park@...sung.com,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        s.nawrocki@...sung.com, myungjoo.ham@...sung.com,
        keescook@...omium.org, tony@...mide.com, jroedel@...e.de,
        treding@...dia.com, digetx@...il.com, willy.mh.wolff.ml@...il.com
Subject: Re: [PATCH v8 08/13] drivers: memory: add DMC driver for Exynos5422

On Thu, 6 Jun 2019 at 12:38, Lukasz Luba <l.luba@...tner.samsung.com> wrote:
> Hi Krzysztof,
> >> +/**
> >> + * exynos5_dmc_init_clks() - Initialize clocks needed for DMC operation.
> >> + * @dmc:       DMC structure containing needed fields
> >> + *
> >> + * Get the needed clocks defined in DT device, enable and set the right parents.
> >> + * Read current frequency and initialize the initial rate for governor.
> >> + */
> >> +static int exynos5_dmc_init_clks(struct exynos5_dmc *dmc)
> >> +{
> >> +       int ret;
> >> +       unsigned long target_volt = 0;
> >> +       unsigned long target_rate = 0;
> >> +
> >> +       dmc->fout_spll = devm_clk_get(dmc->dev, "fout_spll");
> >> +       if (IS_ERR(dmc->fout_spll))
> >> +               return PTR_ERR(dmc->fout_spll);
> >> +
> >> +       dmc->fout_bpll = devm_clk_get(dmc->dev, "fout_bpll");
> >> +       if (IS_ERR(dmc->fout_bpll))
> >> +               return PTR_ERR(dmc->fout_bpll);
> >> +
> >> +       dmc->mout_mclk_cdrex = devm_clk_get(dmc->dev, "mout_mclk_cdrex");
> >> +       if (IS_ERR(dmc->mout_mclk_cdrex))
> >> +               return PTR_ERR(dmc->mout_mclk_cdrex);
> >
> > You are not enabling this clock. It is divider so it is fine for him
> > but what about its parents? How can you guarantee that parents are
> > enabled?
> It uses two parents in this configuration:
> 1. 'mout_bpll' which is set by the bootloader and is a default mode
> 2. 'mout_mx_mspll_ccore' which is used temporary as a 'bypass clock
> source' only for the time when BPLL is changing it's settings
>
> Do you suggest to put a call:
>
> to make sure the parent is up and running?
> OR just move the lines from the end of this function:
>         clk_prepare_enable(dmc->fout_bpll);
>         clk_prepare_enable(dmc->mout_bpll);
> and add:
>         ret = clk_set_parent(dmc->mout_mclk_cdrex, dmc->mout_bpll);
> then call the clk_get_rate on 'mout_mclk_cdrex'
>

Ah, It's my mistake. I missed that later you enable its new parent. It's fine.

Best regards,
Krzysztof