linux-kernel - Re: [PATCH V1] i2c: busses: tegra: Add suspend-resume support

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Date:   Thu, 30 May 2019 14:27:30 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Bitan Biswas <bbiswas@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Shardar Mohammed <smohammed@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>
Subject: Re: [PATCH V1] i2c: busses: tegra: Add suspend-resume support

30.05.2019 8:55, Bitan Biswas пишет:
> Post suspend I2C registers have power on reset values. Before any
> transfer initialize I2C registers to prevent I2C transfer timeout
> and implement suspend and resume callbacks needed. Fix below errors
> post suspend:
> 
> 1) Tegra I2C transfer timeout during jetson tx2 resume:
> 
> [   27.520613] pca953x 1-0074: calling pca953x_resume+0x0/0x1b0 @ 2939, parent: i2c-1
> [   27.633623] tegra-i2c 3160000.i2c: i2c transfer timed out
> [   27.639162] pca953x 1-0074: Unable to sync registers 0x3-0x5. -110
> [   27.645336] pca953x 1-0074: Failed to sync GPIO dir registers: -110
> [   27.651596] PM: dpm_run_callback(): pca953x_resume+0x0/0x1b0 returns -110
> [   27.658375] pca953x 1-0074: pca953x_resume+0x0/0x1b0 returned -110 after 127152 usecs
> [   27.666194] PM: Device 1-0074 failed to resume: error -110
> 
> 2) Tegra I2C transfer timeout error on jetson Xavier post resume.
> 
> Signed-off-by: Bitan Biswas <bbiswas@...dia.com>
> ---
>  drivers/i2c/busses/i2c-tegra.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index ebaa78d..f6a377f 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -1687,9 +1687,33 @@ static int tegra_i2c_remove(struct platform_device *pdev)
>  }
>  
>  #ifdef CONFIG_PM_SLEEP
> +static int tegra_i2c_suspend(struct device *dev)
> +{
> +	struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev);
> +
> +	i2c_mark_adapter_suspended(&i2c_dev->adapter);
> +
> +	return 0;
> +}
> +
> +static int tegra_i2c_resume(struct device *dev)
> +{
> +	struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev);
> +	int ret;
> +
> +	i2c_lock_bus(&i2c_dev->adapter, I2C_LOCK_ROOT_ADAPTER);
> +	ret = tegra_i2c_init(i2c_dev, false);
> +	i2c_unlock_bus(&i2c_dev->adapter, I2C_LOCK_ROOT_ADAPTER);

Why the locking is needed here?

> +	if (!ret)
> +		i2c_mark_adapter_resumed(&i2c_dev->adapter);
> +
> +       return ret;

A very minor nit.. will be a bit more straightforward to write this as:

	int err;

	err = tegra_i2c_init(i2c_dev, false);
	if (err)
		return err;

	i2c_mark_adapter_resumed(&i2c_dev->adapter);

	return 0;

It is always cleaner to return 0 on success.

--
Dmitry