fs: nvs: Improve nvs_calc_free_space() result precision

The nvs_calc_free_space() function does not return 0 when the NVS
is considered full, because some special ATEs are not taken into account.

This commit takes into account the ATE that is reserved for deletion in
each sector, in addition of the 'GC done' ATE when present.

(cherry picked from commit 08496ff)

Original-Signed-off-by: Adrien Ricciardi <aricciardi@baylibre.com>
GitOrigin-RevId: 08496ff
Change-Id: I53ec160b59b5f9038d5ca363367cdc8e6cb7435d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5663173
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Tested-by: Ting Shen <phoenixshen@chromium.org>
Reviewed-by: Ting Shen <phoenixshen@chromium.org>
Commit-Queue: Ting Shen <phoenixshen@chromium.org>

subsys/fs/nvs/nvs.c

@@ -1309,7 +1309,11 @@ ssize_t nvs_calc_free_space(struct nvs_fs *fs)
 
  free_space = 0;
  for (uint16_t i = 1; i < fs->sector_count; i++) {
- free_space += (fs->sector_size - ate_size);
+ /*
+ * There is always a closing ATE and a reserved ATE for
+ * deletion in each sector
+ */
+ free_space += (fs->sector_size - (2 * ate_size));
  }
 
  step_addr = fs->ate_wra;
@@ -1333,11 +1337,17 @@ ssize_t nvs_calc_free_space(struct nvs_fs *fs)
  }
  }
 
- if ((wlk_addr == step_addr) && step_ate.len &&
- (nvs_ate_valid(fs, &step_ate))) {
- /* count needed */
- free_space -= nvs_al_size(fs, step_ate.len);
- free_space -= ate_size;
+ if (nvs_ate_valid(fs, &step_ate)) {
+ /* Take into account the GC done ATE if it is present */
+ if (step_ate.len == 0) {
+ if (step_ate.id == 0xFFFF) {
+ free_space -= ate_size;
+ }
+ } else if (wlk_addr == step_addr) {
+ /* count needed */
+ free_space -= nvs_al_size(fs, step_ate.len);
+ free_space -= ate_size;
+ }
  }
 
  if (step_addr == fs->ate_wra) {