[PATCHi v4] staging: atomisp: move null check to earlier point

From: Cengiz Can
Date: Sat Aug 01 2020 - 17:57:10 EST

`find_gmin_subdev()` that returns a pointer to `struct
gmin_subdev` can return NULL.

In `gmin_v2p8_ctrl()` there's a call to this function but the
possibility of a NULL was not checked before its being dereferenced,

/* Acquired here --------v */
struct gmin_subdev *gs = find_gmin_subdev(subdev);

/* v------Dereferenced here */
if (gs->v2p8_gpio >= 0) {

With this change we're null checking `find_gmin_subdev()` result
and we return an error if that's the case. We also WARN()
for the sake of debugging.

Signed-off-by: Cengiz Can <cengiz@xxxxxxxxxx>
Reported-by: Coverity Static Analyzer CID 1465536
Suggested-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Signed-off-by: Cengiz Can <cengiz@xxxxxxxxxx>

Please do note that this change introduces a new return value to

[NEW] - raise a WARN and return -ENODEV if there are no subdevices.
- return result of `gpio_request` or `gpio_direction_output`.
- return 0 if GPIO is ON.
- return results of `regulator_enable` or `regulator_disable`.
- according to PMIC type, return result of `axp_regulator_set`
or `gmin_i2c_write`.
- return -EINVAL if unknown PMIC type.

Patch Changelog:
v4: Fix minor typo in commit message

drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c b/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
index 0df46a1af5f0..1ad0246764a6 100644
--- a/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
+++ b/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
@@ -871,6 +871,9 @@ static int gmin_v2p8_ctrl(struct v4l2_subdev *subdev, int on)
int ret;
int value;

+ if (WARN_ON(!gs))
+ return -ENODEV;
if (gs->v2p8_gpio >= 0) {
pr_info("atomisp_gmin_platform: 2.8v power on GPIO %d\n",
@@ -881,7 +884,7 @@ static int gmin_v2p8_ctrl(struct v4l2_subdev *subdev, int on)
pr_err("V2P8 GPIO initialization failed\n");

- if (!gs || gs->v2p8_on == on)
+ if (gs->v2p8_on == on)
return 0;
gs->v2p8_on = on;