linux-kernel - Re: [PATCH v3 12/25] clk: bcm: rpi: Use CCF boundaries instead of rolling our own

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Date:   Thu, 04 Jun 2020 20:02:22 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     linux-rpi-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH v3 12/25] clk: bcm: rpi: Use CCF boundaries instead of
 rolling our own

On Wed, 2020-05-27 at 17:45 +0200, Maxime Ripard wrote:
> The raspberrypi firmware clock driver has a min_rate / max_rate clamping by
> storing the info it needs in a private structure.
> 
> However, the CCF already provides such a facility, so we can switch to it
> to remove the boilerplate.
> 
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> ---
>  drivers/clk/bcm/clk-raspberrypi.c | 18 ++++++++----------
>  1 file changed, 8 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/clk/bcm/clk-raspberrypi.c b/drivers/clk/bcm/clk-
> raspberrypi.c
> index a20492fade6a..e135ad28d38d 100644
> --- a/drivers/clk/bcm/clk-raspberrypi.c
> +++ b/drivers/clk/bcm/clk-raspberrypi.c
> @@ -36,9 +36,6 @@ struct raspberrypi_clk {
>  	struct rpi_firmware *firmware;
>  	struct platform_device *cpufreq;
>  
> -	unsigned long min_rate;
> -	unsigned long max_rate;
> -
>  	struct clk_hw pllb;
>  };
>  
> @@ -142,13 +139,11 @@ static int raspberrypi_fw_pll_set_rate(struct clk_hw
> *hw, unsigned long rate,
>  static int raspberrypi_pll_determine_rate(struct clk_hw *hw,
>  					  struct clk_rate_request *req)
>  {
> -	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
> -						   pllb);
>  	u64 div, final_rate;
>  	u32 ndiv, fdiv;
>  
>  	/* We can't use req->rate directly as it would overflow */
> -	final_rate = clamp(req->rate, rpi->min_rate, rpi->max_rate);
> +	final_rate = clamp(req->rate, req->min_rate, req->max_rate);
>  
>  	div = (u64)final_rate << A2W_PLL_FRAC_BITS;
>  	do_div(div, req->best_parent_rate);
> @@ -215,12 +210,15 @@ static int raspberrypi_register_pllb(struct
> raspberrypi_clk *rpi)
>  	dev_info(rpi->dev, "CPU frequency range: min %u, max %u\n",
>  		 min_rate, max_rate);
>  
> -	rpi->min_rate = min_rate * RPI_FIRMWARE_PLLB_ARM_DIV_RATE;
> -	rpi->max_rate = max_rate * RPI_FIRMWARE_PLLB_ARM_DIV_RATE;
> -
>  	rpi->pllb.init = &init;
>  
> -	return devm_clk_hw_register(rpi->dev, &rpi->pllb);
> +	ret = devm_clk_hw_register(rpi->dev, &rpi->pllb);
> +	if (!ret)
> +		clk_hw_set_rate_range(&rpi->pllb,
> +				      min_rate * RPI_FIRMWARE_PLLB_ARM_DIV_RATE,
> +				      max_rate *
> RPI_FIRMWARE_PLLB_ARM_DIV_RATE);

Isn't there a potential race here? Albeit unlikely, cpufreq could show up and
call clk_round_rate() in between the registration and you setting the ranges.

Regards,
Nicolas



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