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| author | Kent Gibson <warthog618@gmail.com> | 2023-12-19 08:41:58 +0800 |
|---|---|---|
| committer | Bartosz Golaszewski <bartosz.golaszewski@linaro.org> | 2023-12-19 10:18:49 +0100 |
| commit | 193b6b0902bf57ff13bbadaa037a288c73c9d126 (patch) | |
| tree | dbb83461a355cb736e78c363bd320e47ef8562a8 /drivers/gpio | |
| parent | 0ebeaab4d59eb373e17ffbc50d8c4e9665418cbe (diff) | |
| download | lwn-193b6b0902bf57ff13bbadaa037a288c73c9d126.tar.gz lwn-193b6b0902bf57ff13bbadaa037a288c73c9d126.zip | |
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>
Diffstat (limited to 'drivers/gpio')
| -rw-r--r-- | drivers/gpio/gpiolib-cdev.c | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c index 84471b703402..e3fdf7b86d10 100644 --- a/drivers/gpio/gpiolib-cdev.c +++ b/drivers/gpio/gpiolib-cdev.c @@ -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; |