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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: Kent Gibson <warthog618@gmail.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
This commit is contained in:
Kent Gibson 2023-12-19 08:41:58 +08:00 committed by Bartosz Golaszewski
parent 0ebeaab4d5
commit 193b6b0902
1 changed files with 23 additions and 1 deletions
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24
drivers/gpio/gpiolib-cdev.c
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@ -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;