linux-kernel - Re: [PATCH 04/49] iio: fix opencoded for_each_set

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Message-ID: <2d5e9096-e40d-13af-234a-539108df1c50@wanadoo.fr>
Date:   Fri, 11 Feb 2022 18:17:37 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Laight <David.Laight@...lab.com>,
        Joe Perches <joe@...ches.com>, Dennis Zhou <dennis@...nel.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Nicholas Piggin <npiggin@...il.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Alexey Klimov <aklimov@...hat.com>,
        linux-kernel@...r.kernel.org, Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-iio@...r.kernel.org
Subject: Re: [PATCH 04/49] iio: fix opencoded for_each_set_bit()

Le 10/02/2022 à 23:48, Yury Norov a écrit :
> iio_simple_dummy_trigger_h() is mostly an opencoded for_each_set_bit().
> Using for_each_set_bit() make code much cleaner, and more effective.
> 
> Signed-off-by: Yury Norov <yury.norov-Re5JQEeQqe8AvxtiuMwx3w@...lic.gmane.org>
> ---
>   drivers/iio/dummy/iio_simple_dummy_buffer.c | 48 ++++++++-------------
>   1 file changed, 19 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/iio/dummy/iio_simple_dummy_buffer.c b/drivers/iio/dummy/iio_simple_dummy_buffer.c
> index d81c2b2dad82..3bc1b7529e2a 100644
> --- a/drivers/iio/dummy/iio_simple_dummy_buffer.c
> +++ b/drivers/iio/dummy/iio_simple_dummy_buffer.c
> @@ -45,41 +45,31 @@ static irqreturn_t iio_simple_dummy_trigger_h(int irq, void *p)
>   {
>   	struct iio_poll_func *pf = p;
>   	struct iio_dev *indio_dev = pf->indio_dev;
> +	int i = 0, j;
>   	u16 *data;
>   
>   	data = kmalloc(indio_dev->scan_bytes, GFP_KERNEL);
>   	if (!data)
>   		goto done;
>   
> -	if (!bitmap_empty(indio_dev->active_scan_mask, indio_dev->masklength)) {
> -		/*
> -		 * Three common options here:
> -		 * hardware scans: certain combinations of channels make
> -		 *   up a fast read.  The capture will consist of all of them.
> -		 *   Hence we just call the grab data function and fill the
> -		 *   buffer without processing.
> -		 * software scans: can be considered to be random access
> -		 *   so efficient reading is just a case of minimal bus
> -		 *   transactions.
> -		 * software culled hardware scans:
> -		 *   occasionally a driver may process the nearest hardware
> -		 *   scan to avoid storing elements that are not desired. This
> -		 *   is the fiddliest option by far.
> -		 * Here let's pretend we have random access. And the values are
> -		 * in the constant table fakedata.
> -		 */
> -		int i, j;
> -
> -		for (i = 0, j = 0;
> -		     i < bitmap_weight(indio_dev->active_scan_mask,
> -				       indio_dev->masklength);
> -		     i++, j++) {
> -			j = find_next_bit(indio_dev->active_scan_mask,
> -					  indio_dev->masklength, j);
> -			/* random access read from the 'device' */
> -			data[i] = fakedata[j];
> -		}
> -	}
> +	/*
> +	 * Three common options here:
> +	 * hardware scans: certain combinations of channels make
> +	 *   up a fast read.  The capture will consist of all of them.
> +	 *   Hence we just call the grab data function and fill the
> +	 *   buffer without processing.
> +	 * software scans: can be considered to be random access
> +	 *   so efficient reading is just a case of minimal bus
> +	 *   transactions.
> +	 * software culled hardware scans:
> +	 *   occasionally a driver may process the nearest hardware
> +	 *   scan to avoid storing elements that are not desired. This
> +	 *   is the fiddliest option by far.
> +	 * Here let's pretend we have random access. And the values are
> +	 * in the constant table fakedata.
> +	 */

Nitpicking: you could take advantage of the tab you save to use the full 
width of the line and save some lines of code.

Just my 2c.

CJ


> +	for_each_set_bit(j, indio_dev->active_scan_mask, indio_dev->masklength)
> +		data[i++] = fakedata[j];
>   
>   	iio_push_to_buffers_with_timestamp(indio_dev, data,
>   					   iio_get_time_ns(indio_dev));