linux-kernel - Re: [RESEND PATCH v7 5/5] clk: ti: add am33xx/am43xx spread spectrum clock support

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Message-ID: <162319994979.1835121.15194981692038400158@swboyd.mtv.corp.google.com>
Date:   Tue, 08 Jun 2021 17:52:29 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Dario Binacchi <dariobin@...ero.it>, linux-clk@...r.kernel.org
Cc:     Rob Herring <robh@...nel.org>, Tony Lindgren <tony@...mide.com>,
        Michael Turquette <mturquette@...libre.com>,
        Dario Binacchi <dariobin@...ero.it>,
        linux-omap@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Benoît Cousson <bcousson@...libre.com>,
        Tero Kristo <kristo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v7 5/5] clk: ti: add am33xx/am43xx spread spectrum clock support

Quoting Dario Binacchi (2021-06-06 13:22:53)
> The patch enables spread spectrum clocking (SSC) for MPU and LCD PLLs.
> As reported by the TI spruh73x/spruhl7x RM, SSC is only supported for
> the DISP/LCD and MPU PLLs on am33xx/am43xx. SSC is not supported for
> DDR, PER, and CORE PLLs.
> 
> Calculating the required values and setting the registers accordingly
> was taken from the set_mpu_spreadspectrum routine contained in the
> arch/arm/mach-omap2/am33xx/clock_am33xx.c file of the u-boot project.
> 
> In locked condition, DPLL output clock = CLKINP *[M/N]. In case of
> SSC enabled, the reference manual explains that there is a restriction
> of range of M values. Since the omap2_dpll_round_rate routine attempts
> to select the minimum possible N, the value of M obtained is not
> guaranteed to be within the range required. With the new "ti,min-div"
> parameter it is possible to increase N and consequently M to satisfy the
> constraint imposed by SSC.
> 
> Signed-off-by: Dario Binacchi <dariobin@...ero.it>
> Reviewed-by: Tero Kristo <kristo@...nel.org>
> 
> ---

Applied to clk-next