linux-kernel - Re: [V3][PATCH] clk: zynqmp: pll: add set_pll_mode to check condition in zynqmp_pll

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Date:   Wed, 07 Apr 2021 18:09:37 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Michael Turquette <mturquette@...libre.com>,
        Michal Simek <michal.simek@...inx.com>,
        quanyang.wang@...driver.com
Cc:     Rajan Vaja <rajan.vaja@...inx.com>,
        Jolly Shah <jolly.shah@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Quanyang Wang <quanyang.wang@...driver.com>,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [V3][PATCH] clk: zynqmp: pll: add set_pll_mode to check condition in zynqmp_pll_enable

Quoting quanyang.wang@...driver.com (2021-04-06 08:31:31)
> From: Quanyang Wang <quanyang.wang@...driver.com>
> 
> If there is a IOCTL_SET_PLL_FRAC_MODE request sent to ATF ever,
> we shouldn't skip invoking PM_CLOCK_ENABLE fn even though this
> pll has been enabled. In ATF implementation, it will only assign
> the mode to the variable (struct pm_pll *)pll->mode when handling
> IOCTL_SET_PLL_FRAC_MODE call. Invoking PM_CLOCK_ENABLE can force
> ATF send request to PWU to set the pll mode to PLL's register.
> 
> There is a scenario that happens in enabling VPLL_INT(clk_id:96):
> 1) VPLL_INT has been enabled during booting.
> 2) A driver calls clk_set_rate and according to the rate, the VPLL_INT
>    should be set to FRAC mode. Then zynqmp_pll_set_mode is called
>    to pass IOCTL_SET_PLL_FRAC_MODE to ATF. Note that at this point
>    ATF just stores the mode to a variable.
> 3) This driver calls clk_prepare_enable and zynqmp_pll_enable is
>    called to try to enable VPLL_INT pll. Because of 1), the function
>    zynqmp_pll_enable just returns without doing anything after checking
>    that this pll has been enabled.
> 
> In the scenario above, the pll mode of VPLL_INT will never be set
> successfully. So adding set_pll_mode to check condition to fix it.
> 
> Fixes: 3fde0e16d016 ("drivers: clk: Add ZynqMP clock driver")
> Signed-off-by: Quanyang Wang <quanyang.wang@...driver.com>
> Tested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> ---

Applied to clk-next