linux-kernel - Re: [PATCH v6 1/4] gpiolib: Pass bitmaps, not integer arrays, to get/set array

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Date:   Sat, 1 Sep 2018 02:23:17 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Jonathan Corbet <corbet@....net>,
        Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Peter Korsgaard <peter.korsgaard@...co.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Jiri Slaby <jslaby@...e.com>, Willy Tarreau <w@....eu>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-doc@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-mmc@...r.kernel.org, netdev@...r.kernel.org,
        linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-serial@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/4] gpiolib: Pass bitmaps, not integer arrays, to
 get/set array

On 2018-09-01 00:56, Janusz Krzysztofik wrote:
> Most users of get/set array functions iterate consecutive bits of data,
> usually a single integer, while processing array of results obtained
> from, or building an array of values to be passed to those functions.
> Save time wasted on those iterations by changing the functions' API to
> accept bitmaps.
> 
> All current users are updated as well.
> 
> More benefits from the change are expected as soon as planned support
> for accepting/passing those bitmaps directly from/to respective GPIO
> chip callbacks if applicable is implemented.

> diff --git a/drivers/i2c/muxes/i2c-mux-gpio.c b/drivers/i2c/muxes/i2c-mux-gpio.c
> index 401308e3d036..e28ddc20000d 100644
> --- a/drivers/i2c/muxes/i2c-mux-gpio.c
> +++ b/drivers/i2c/muxes/i2c-mux-gpio.c
> @@ -22,18 +22,16 @@ struct gpiomux {
>  	struct i2c_mux_gpio_platform_data data;
>  	unsigned gpio_base;
>  	struct gpio_desc **gpios;
> -	int *values;
>  };
>  
>  static void i2c_mux_gpio_set(const struct gpiomux *mux, unsigned val)
>  {
> -	int i;
> -
> -	for (i = 0; i < mux->data.n_gpios; i++)
> -		mux->values[i] = (val >> i) & 1;
> +	DECLARE_BITMAP(value_bitmap, mux->data.n_gpios);

Picking a random driver for this comment, it applies to many of them.

I think this creates a VLA? Can't you, for the bit-count, just go with
BITS_PER_TYPE(unsigned)? Or whatever is appropriate for the driver
in question.

Also, I find that where you use DECLARE_BITMAP, the _bitmap suffix is
just noise and I would very much like to zap it.

Cheers,
Peter

> +	
> +	*value_bitmap = val;
>  
>  	gpiod_set_array_value_cansleep(mux->data.n_gpios,
> -				       mux->gpios, mux->values);
> +				       mux->gpios, value_bitmap);
>  }
>  
>  static int i2c_mux_gpio_select(struct i2c_mux_core *muxc, u32 chan)
> @@ -182,15 +180,13 @@ static int i2c_mux_gpio_probe(struct platform_device *pdev)
>  		return -EPROBE_DEFER;
>  
>  	muxc = i2c_mux_alloc(parent, &pdev->dev, mux->data.n_values,
> -			     mux->data.n_gpios * sizeof(*mux->gpios) +
> -			     mux->data.n_gpios * sizeof(*mux->values), 0,
> +			     mux->data.n_gpios * sizeof(*mux->gpios), 0,
>  			     i2c_mux_gpio_select, NULL);
>  	if (!muxc) {
>  		ret = -ENOMEM;
>  		goto alloc_failed;
>  	}
>  	mux->gpios = muxc->priv;
> -	mux->values = (int *)(mux->gpios + mux->data.n_gpios);
>  	muxc->priv = mux;
>  
>  	platform_set_drvdata(pdev, muxc);