linux-kernel - Re: [PATCH 3/5] i2c-mux-gpio: Save initial channel number to the idle data field

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Message-ID: <7c8d4751-f5f7-ee2a-c411-a985b81d61a3@axentia.se>
Date:   Wed, 24 Apr 2019 21:26:22 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     Serge Semin <fancer.lancer@...il.com>,
        Peter Korsgaard <peter.korsgaard@...co.com>
CC:     Serge Semin <Sergey.Semin@...latforms.ru>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] i2c-mux-gpio: Save initial channel number to the idle
 data field

On 2019-04-24 14:34, Serge Semin wrote:
> In case if the idle state has been specified in the data structure,
> the idle variable is left untouched as before, so to keep a default
> channel number enabled in the mux idle state. But if a platform doesn't
> specify which channel is going to be enabled by default, we as before
> don't setup the deselect callback, but the initial state is saved in the
> idle variable for further initialization. We can safely do this here
> since that variable is used for initial state setting only, when no
> idling lane is specified.

While this subtlety is *maybe* ok, a comment about it belongs in the
*code* where it will be seen when the next person makes changes.

But why not extend the struct with the initial state? How many of
these muxes do you expect to exist in a system? Multiplied by a
couple of bytes. Who cares?

Cheers,
Peter

> 
> The reason of this change is to prepare the code for future GPIOs request
> path being split up into of- and plat- based methods. The idle variable
> here is used as a container of the initial state for both of the paths in
> case of idle-channel isn't specified.
> 
> Signed-off-by: Serge Semin <fancer.lancer@...il.com>
> ---
>  drivers/i2c/muxes/i2c-mux-gpio.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-gpio.c b/drivers/i2c/muxes/i2c-mux-gpio.c
> index a14fe132b0c3..535c83c43371 100644
> --- a/drivers/i2c/muxes/i2c-mux-gpio.c
> +++ b/drivers/i2c/muxes/i2c-mux-gpio.c
> @@ -171,7 +171,6 @@ static int i2c_mux_gpio_probe(struct platform_device *pdev)
>  	struct gpiomux *mux;
>  	struct i2c_adapter *parent;
>  	struct i2c_adapter *root;
> -	unsigned initial_state;
>  	int i, ret;
>  
>  	mux = devm_kzalloc(&pdev->dev, sizeof(*mux), GFP_KERNEL);
> @@ -204,12 +203,14 @@ static int i2c_mux_gpio_probe(struct platform_device *pdev)
>  
>  	muxc->mux_locked = true;
>  
> -	if (mux->data.idle != I2C_MUX_GPIO_NO_IDLE) {
> -		initial_state = mux->data.idle;
> +	/*
> +	 * Set descelect callback if idle state has been setup otherwise just
> +	 * use the idle variable to store the initial muxer value.
> +	 */
> +	if (mux->data.idle != I2C_MUX_GPIO_NO_IDLE)
>  		muxc->deselect = i2c_mux_gpio_deselect;
> -	} else {
> -		initial_state = mux->data.values[0];
> -	}
> +	else
> +		mux->data.idle = mux->data.values[0];
>  
>  	for (i = 0; i < mux->data.n_gpios; i++) {
>  		struct device *gpio_dev;
> @@ -224,7 +225,7 @@ static int i2c_mux_gpio_probe(struct platform_device *pdev)
>  		}
>  
>  		ret = gpio_direction_output(mux->gpio_base + mux->data.gpios[i],
> -					    initial_state & (1 << i));
> +					    mux->data.idle & (1 << i));
>  		if (ret) {
>  			dev_err(&pdev->dev,
>  				"Failed to set direction of GPIO %d to output\n",
>