linux-kernel - Re: [PATCH v2 03/19] PM / devfreq: tegra: Don't ignore clk errors

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Date:   Tue, 16 Apr 2019 10:52:44 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:     linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 03/19] PM / devfreq: tegra: Don't ignore clk errors

Hi,

On 19. 4. 15. 오후 11:54, Dmitry Osipenko wrote:
> The clk_set_min_rate() could fail and in this case clk_set_rate() sets
> rate to 0, which may drop EMC rate to minimum and make machine very
> difficult to use.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/devfreq/tegra-devfreq.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/devfreq/tegra-devfreq.c b/drivers/devfreq/tegra-devfreq.c
> index 0c0909fba545..69581c9082d4 100644
> --- a/drivers/devfreq/tegra-devfreq.c
> +++ b/drivers/devfreq/tegra-devfreq.c
> @@ -487,6 +487,7 @@ static int tegra_devfreq_target(struct device *dev, unsigned long *freq,
>  	struct tegra_devfreq *tegra = dev_get_drvdata(dev);
>  	struct dev_pm_opp *opp;
>  	unsigned long rate;
> +	int err;
>  
>  	opp = devfreq_recommended_opp(dev, freq, flags);
>  	if (IS_ERR(opp)) {
> @@ -496,8 +497,13 @@ static int tegra_devfreq_target(struct device *dev, unsigned long *freq,
>  	rate = dev_pm_opp_get_freq(opp);
>  	dev_pm_opp_put(opp);
>  
> -	clk_set_min_rate(tegra->emc_clock, rate);
> -	clk_set_rate(tegra->emc_clock, 0);
> +	err = clk_set_min_rate(tegra->emc_clock, rate);
> +	if (err)
> +		return err;
> +
> +	err = clk_set_rate(tegra->emc_clock, 0);
> +	if (err)

Why don't you restore the previous minimum clock for tegra->emc_clock
when failed to execute 'clk_set_rate(tegra->emc_clock, 0);'?

I think that if you control the restoring the previous minimum clock,
it is more nice to handle the error handling.

> +		return err;
>  
>  	return 0;
>  }
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics