linux-kernel - Re: [PATCH] devfreq: exynos-bus: workaround dev_pm_opp_set

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Date:   Thu, 10 Oct 2019 11:50:13 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     k.konieczny@...tner.samsung.com
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-pm@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] devfreq: exynos-bus: workaround dev_pm_opp_set_rate()
 errors on Exynos5422/5800 SoCs

On 2019년 10월 08일 22:49, k.konieczny@...tner.samsung.com wrote:
> Commit 4294a779bd8d ("PM / devfreq: exynos-bus: Convert to use
> dev_pm_opp_set_rate()") introduced errors:
> exynos-bus: new bus device registered: soc:bus_wcore ( 84000 KHz ~ 400000 KHz)
> exynos-bus: new bus device registered: soc:bus_noc ( 67000 KHz ~ 100000 KHz)
> exynos-bus: new bus device registered: soc:bus_fsys_apb (100000 KHz ~ 200000 KHz)
> ...
> exynos-bus soc:bus_wcore: dev_pm_opp_set_rate: failed to find current OPP for freq 532000000 (-34)
> exynos-bus soc:bus_noc: dev_pm_opp_set_rate: failed to find current OPP for freq 111000000 (-34)
> exynos-bus soc:bus_fsys_apb: dev_pm_opp_set_rate: failed to find current OPP for freq 222000000 (-34)
> 
> They are caused by incorrect PLL assigned to clock source, which results
> in clock rate outside of OPP range. Add workaround for this in
> exynos_bus_parse_of() by adjusting clock rate to those present in OPP.

If the clock caused this issue, you can set the initial clock on DeviceTree
with assigned-clock-* properties. Because the probe time of clock driver
is early than the any device drivers.

It is not proper to fix the clock issue on other device driver.
I think you can fix it by using the supported clock properties.


> 
> Fixes: 4294a779bd8d ("PM / devfreq: exynos-bus: Convert to use dev_pm_opp_set_rate()")
> Reported-by: Krzysztof Kozlowski <krzk@...nel.org>
> Signed-off-by: Kamil Konieczny <k.konieczny@...tner.samsung.com>
> ---
>  drivers/devfreq/exynos-bus.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/devfreq/exynos-bus.c b/drivers/devfreq/exynos-bus.c
> index c832673273a2..37bd34d5625b 100644
> --- a/drivers/devfreq/exynos-bus.c
> +++ b/drivers/devfreq/exynos-bus.c
> @@ -243,7 +243,7 @@ static int exynos_bus_parse_of(struct device_node *np,
>  {
>  	struct device *dev = bus->dev;
>  	struct dev_pm_opp *opp;
> -	unsigned long rate;
> +	unsigned long rate, opp_rate;
>  	int ret;
>  
>  	/* Get the clock to provide each bus with source clock */
> @@ -267,13 +267,21 @@ static int exynos_bus_parse_of(struct device_node *np,
>  	}
>  
>  	rate = clk_get_rate(bus->clk);
> -
> -	opp = devfreq_recommended_opp(dev, &rate, 0);
> +	opp_rate = rate;
> +	opp = devfreq_recommended_opp(dev, &opp_rate, 0);
>  	if (IS_ERR(opp)) {
>  		dev_err(dev, "failed to find dev_pm_opp\n");
>  		ret = PTR_ERR(opp);
>  		goto err_opp;
>  	}
> +	/*
> +	 * FIXME: U-boot leaves clock source at incorrect PLL, this results
> +	 * in clock rate outside defined OPP rate. Work around this bug by
> +	 * setting clock rate to recommended one.
> +	 */
> +	if (rate > opp_rate)
> +		clk_set_rate(bus->clk, opp_rate);
> +
>  	bus->curr_freq = dev_pm_opp_get_freq(opp);
>  	dev_pm_opp_put(opp);
>  
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics