linux-kernel - Re: [RESEND PATCH v4 3/8] gpio: 104-dio-48e: Utilize for_each_set

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Message-ID: <822be05b-092b-41c2-3c31-8981acd5cb9e@rasmusvillemoes.dk>
Date:   Tue, 2 Oct 2018 09:00:45 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     William Breathitt Gray <vilhelm.gray@...il.com>,
        linus.walleij@...aro.org, akpm@...ux-foundation.org
Cc:     linux-gpio@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, andriy.shevchenko@...ux.intel.com
Subject: Re: [RESEND PATCH v4 3/8] gpio: 104-dio-48e: Utilize
 for_each_set_clump macro

On 2018-10-02 03:14, William Breathitt Gray wrote:
>  	/* clear bits array to a clean slate */
>  	bitmap_zero(bits, chip->ngpio);
>  
> -	/* get bits are evaluated a gpio port register at a time */
> -	for (i = 0; i < ARRAY_SIZE(ports); i++) {
> -		/* gpio offset in bits array */
> -		bits_offset = i * gpio_reg_size;
> -
> -		/* word index for bits array */
> -		word_index = BIT_WORD(bits_offset);
> -
> -		/* gpio offset within current word of bits array */
> -		word_offset = bits_offset % BITS_PER_LONG;
> -
> -		/* mask of get bits for current gpio within current word */
> -		word_mask = mask[word_index] & (port_mask << word_offset);
> -		if (!word_mask) {
> -			/* no get bits in this port so skip to next one */
> -			continue;
> -		}
> -
> -		/* read bits from current gpio port */
> +	for_each_set_clump(i, word, offset, mask, ARRAY_SIZE(ports), 8) {
>  		port_state = inb(dio48egpio->base + ports[i]);
> -
> -		/* store acquired bits at respective bits array offset */
> -		bits[word_index] |= port_state << word_offset;
> +		bits[word] |= port_state << offset;

Somewhat unrelated to this series, but is the existing code correct? I'd
expect the RHS to be masked by word_mask; otherwise we might set bits in
bits[] that were not requested? And if one does that, the !word_mask
test is merely an optimization to avoid reading the gpios when the
result would be ignored anyway. Perhaps no caller cares.

Rasmus