Commit 193b6b09 authored by Kent Gibson's avatar Kent Gibson Committed by Bartosz Golaszewski
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gpiolib: cdev: improve documentation of get/set values 



Add documentation of the algorithm used to perform scatter/gather
of the requested lines and values in linereq_get_values() and
linereq_set_values_unlocked() to improve maintainability.

Signed-off-by: default avatarKent Gibson <warthog618@gmail.com>
Reviewed-by: default avatarAndy Shevchenko <andy@kernel.org>
Signed-off-by: default avatarBartosz Golaszewski <bartosz.golaszewski@linaro.org>
parent 0ebeaab4

drivers/gpio/gpiolib-cdev.c

+23 −1
Original line number Diff line number Diff line
@@ -1394,9 +1394,18 @@ static long linereq_get_values(struct linereq *lr, void __user *ip) 
	if (copy_from_user(&lv, ip, sizeof(lv)))

		return -EFAULT;



	/*

	 * gpiod_get_array_value_complex() requires compacted desc and val

	 * arrays, rather than the sparse ones in lv.

	 * Calculation of num_get and construction of the desc array is

	 * optimized to avoid allocation for the desc array for the common

	 * num_get == 1 case.

	 */

	/* scan requested lines to calculate the subset to get */

	for (num_get = 0, i = 0; i < lr->num_lines; i++) {

		if (lv.mask & BIT_ULL(i)) {

			num_get++;

			/* capture desc for the num_get == 1 case */

			descs = &lr->lines[i].desc;

		}

	}
@@ -1405,6 +1414,7 @@ static long linereq_get_values(struct linereq *lr, void __user *ip) 
		return -EINVAL;



	if (num_get != 1) {

		/* build compacted desc array */

		descs = kmalloc_array(num_get, sizeof(*descs), GFP_KERNEL);

		if (!descs)

			return -ENOMEM;
@@ -1425,6 +1435,7 @@ static long linereq_get_values(struct linereq *lr, void __user *ip) 


	lv.bits = 0;

	for (didx = 0, i = 0; i < lr->num_lines; i++) {

		/* unpack compacted vals for the response */

		if (lv.mask & BIT_ULL(i)) {

			if (lr->lines[i].sw_debounced)

				val = debounced_value(&lr->lines[i]);
@@ -1450,14 +1461,25 @@ static long linereq_set_values_unlocked(struct linereq *lr, 
	unsigned int i, didx, num_set;

	int ret;



	/*

	 * gpiod_set_array_value_complex() requires compacted desc and val

	 * arrays, rather than the sparse ones in lv.

	 * Calculation of num_set and construction of the descs and vals arrays

	 * is optimized to minimize scanning the lv->mask, and to avoid

	 * allocation for the desc array for the common num_set == 1 case.

	 */

	bitmap_zero(vals, GPIO_V2_LINES_MAX);

	/* scan requested lines to determine the subset to be set */

	for (num_set = 0, i = 0; i < lr->num_lines; i++) {

		if (lv->mask & BIT_ULL(i)) {

			/* setting inputs is not allowed */

			if (!test_bit(FLAG_IS_OUT, &lr->lines[i].desc->flags))

				return -EPERM;

			/* add to compacted values */

			if (lv->bits & BIT_ULL(i))

				__set_bit(num_set, vals);

			num_set++;

			/* capture desc for the num_set == 1 case */

			descs = &lr->lines[i].desc;

		}

	}
@@ -1465,7 +1487,7 @@ static long linereq_set_values_unlocked(struct linereq *lr, 
		return -EINVAL;



	if (num_set != 1) {

		/* build compacted desc array and values */

		/* build compacted desc array */

		descs = kmalloc_array(num_set, sizeof(*descs), GFP_KERNEL);

		if (!descs)

			return -ENOMEM;