`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,
i.e.:

  /* 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 <cen...@kernel.wtf>
Reported-by: Coverity Static Analyzer CID 1465536
Suggested-by: Mauro Carvalho Chehab <mche...@kernel.org>
Signed-off-by: Cengiz Can <cen...@kernel.wtf>
---

 Please do note that this change introduces a new return value to
 `gmin_v2p8_ctrl()`.

 [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
   v5: Remove typo from email subject

 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",
                        gs->v2p8_gpio);
@@ -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;
 
-- 
2.27.0

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