linux-kernel - Re: [PATCH 3/6] clk: samsung: clk-pll: Implement pll0831x PLL type

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Message-ID: <4a6e73bb-617d-d849-d64a-7f0de46ea03b@canonical.com>
Date:   Wed, 15 Sep 2021 10:26:07 +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 3/6] clk: samsung: clk-pll: Implement pll0831x PLL type

On 14/09/2021 17:56, Sam Protsenko wrote:
> pll0831x PLL is used in Exynos850 SoC for top-level fractional PLLs. The
> code was derived from very similar pll36xx type, with next differences:
> 
> 1. Lock time for pll0831x is 500*P_DIV, when for pll36xx it's 3000*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 pll36xx
>    implementation)
> 3. The offset from PMS-values register to K-value register is 0x8 for
>    pll0831x, when for pll36xx it's 0x4
> 
> When defining pll0831x type, CON3 register offset should be provided as
> a "con" parameter of PLL() macro, like this:
> 
>     PLL(pll_0831x, 0, "fout_mmc_pll", "oscclk",
>         PLL_LOCKTIME_PLL_MMC, PLL_CON3_PLL_MMC, pll0831x_26mhz_tbl),
> 
> To define PLL rates table, one can use PLL_36XX_RATE() macro, e.g.:
> 
>     PLL_36XX_RATE(26 * MHZ, 799999877, 31, 1, 0, -15124)
> 
> as it's completely appropriate for pl0831x 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_mmc_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 | 105 ++++++++++++++++++++++++++++++++++
>  drivers/clk/samsung/clk-pll.h |   1 +
>  2 files changed, 106 insertions(+)
> 


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


Best regards,
Krzysztof