linux-kernel - Re: [PATCH 2/6] clk: samsung: clk-pll: Implement pll0822x PLL type

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Date:   Wed, 15 Sep 2021 10:24:33 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Paweł Chmiel <pawel.mikolaj.chmiel@...il.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Tomasz Figa <tomasz.figa@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>
Cc:     Ryu Euiyoul <ryu.real@...sung.com>, Tom Gall <tom.gall@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Amit Pundir <amit.pundir@...aro.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 2/6] clk: samsung: clk-pll: Implement pll0822x PLL type

On 14/09/2021 17:56, Sam Protsenko wrote:
> pll0822x PLL is used in Exynos850 SoC for top-level integer PLLs. The
> code was derived from very similar pll35xx type, with next differences:
> 
> 1. Lock time for pll0822x is 150*P_DIV, when for pll35xx it's 270*P_DIV
> 2. It's not suggested in Exynos850 TRM that S_DIV change doesn't require
>    performing PLL lock procedure (which is done in pll35xx
>    implementation)
> 
> When defining pll0822x type, CON3 register offset should be provided as
> a "con" parameter of PLL() macro, like this:
> 
>     PLL(pll_0822x, 0, "fout_shared0_pll", "oscclk",
>         PLL_LOCKTIME_PLL_SHARED0, PLL_CON3_PLL_SHARED0,
>         exynos850_shared0_pll_rates),
> 
> To define PLL rates table, one can use PLL_35XX_RATE() macro, e.g.:
> 
>     PLL_35XX_RATE(26 * MHZ, 1600 * MHZ, 800, 13, 0)
> 
> as it's completely appropriate for pl0822x type and there is no sense in
> duplicating that.
> 
> If bit #1 (MANUAL_PLL_CTRL) is not set in CON1 register, it won't be
> possible to set new rate, with next error showing in kernel log:
> 
>     Could not lock PLL fout_shared1_pll
> 
> That can happen for example if bootloader clears that bit beforehand.
> PLL driver doesn't account for that, so if MANUAL_PLL_CTRL bit was
> cleared, it's assumed it was done for a reason and it shouldn't be
> possible to change that PLL's rate at all.
> 
> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> ---
>  drivers/clk/samsung/clk-pll.c | 91 +++++++++++++++++++++++++++++++++++
>  drivers/clk/samsung/clk-pll.h |  1 +
>  2 files changed, 92 insertions(+)
> 


Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>


Best regards,
Krzysztof