Take the panel reference and put it back as required
using the helpers introduced in previous patch.
drm_panel_add() and drm_panel_remove()
add a panel to the global registry and removes a panel
respectively, use get() and put() helpers to keep up
with refcounting.

Signed-off-by: Anusha Srivatsa <asrivats@redhat.com>
---
 drivers/gpu/drm/drm_panel.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index 079c3c666a2ddc99a0051d1a3c9ba65d986dd003..11a0415bc61f59190ef5eb378d1583c493265e6a 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -79,6 +79,7 @@ EXPORT_SYMBOL(drm_panel_init);
  */
 void drm_panel_add(struct drm_panel *panel)
 {
+	drm_panel_get(panel);
 	mutex_lock(&panel_lock);
 	list_add_tail(&panel->list, &panel_list);
 	mutex_unlock(&panel_lock);
@@ -96,6 +97,7 @@ void drm_panel_remove(struct drm_panel *panel)
 	mutex_lock(&panel_lock);
 	list_del_init(&panel->list);
 	mutex_unlock(&panel_lock);
+	drm_panel_put(panel);
 }
 EXPORT_SYMBOL(drm_panel_remove);
 

-- 
2.48.1

On Tue, Mar 25, 2025 at 01:24:10PM -0400, Anusha Srivatsa wrote:
> Take the panel reference and put it back as required
> using the helpers introduced in previous patch.
> drm_panel_add() and drm_panel_remove()
> add a panel to the global registry and removes a panel
> respectively, use get() and put() helpers to keep up
> with refcounting.
> 
> Signed-off-by: Anusha Srivatsa <asrivats@redhat.com>

We should defer merging that patch until we have converted all the panel
drivers to the new allocation function.

Maxime

On Tue, 25 Mar 2025 13:24:10 -0400
Anusha Srivatsa <asrivats@redhat.com> wrote:

> Take the panel reference and put it back as required
> using the helpers introduced in previous patch.
> drm_panel_add() and drm_panel_remove()
> add a panel to the global registry and removes a panel
> respectively, use get() and put() helpers to keep up
> with refcounting.
> 
> Signed-off-by: Anusha Srivatsa <asrivats@redhat.com>

This is OK but is should not be applied until all panel drivers are
converted to the new devm_drm_panel_alloc() API. Otherwise for
not-yet-converted panel drivers drm_panel_get/put() would operate on an
uninitialized kref. See [0].

# Do not apply until all panel drivers are converted!
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

[0] https://lore.kernel.org/all/20250317155607.68cff522@booty/

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Hi Anusha,

kernel test robot noticed the following build errors:

[auto build test ERROR on c8ba07caaecc622a9922cda49f24790821af8a71]

url:    https://github.com/intel-lab-lkp/linux/commits/Anusha-Srivatsa/drm-panel-Add-new-helpers-for-refcounted-panel-allocatons/20250326-012651
base:   c8ba07caaecc622a9922cda49f24790821af8a71
patch link:    https://lore.kernel.org/r/20250325-b4-panel-refcounting-v1-3-4e2bf5d19c5d%40redhat.com
patch subject: [PATCH 3/5] drm/panel: get/put panel reference in drm_panel_add/remove()
config: hexagon-randconfig-002-20250326 (https://download.01.org/0day-ci/archive/20250326/202503261119.h0EEYLFA-lkp@intel.com/config)
compiler: clang version 21.0.0git (https://github.com/llvm/llvm-project c2692afc0a92cd5da140dfcdfff7818a5b8ce997)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250326/202503261119.h0EEYLFA-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202503261119.h0EEYLFA-lkp@intel.com/

All errors (new ones prefixed by >>):

>> ld.lld: error: undefined symbol: drm_panel_get
   >>> referenced by drm_panel.c:82 (drivers/gpu/drm/drm_panel.c:82)
   >>>               drivers/gpu/drm/drm_panel.o:(drm_panel_add) in archive vmlinux.a
   >>> referenced by drm_panel.c:82 (drivers/gpu/drm/drm_panel.c:82)
   >>>               drivers/gpu/drm/drm_panel.o:(drm_panel_add) in archive vmlinux.a
--
>> ld.lld: error: undefined symbol: drm_panel_put
   >>> referenced by drm_panel.c:100 (drivers/gpu/drm/drm_panel.c:100)
   >>>               drivers/gpu/drm/drm_panel.o:(drm_panel_remove) in archive vmlinux.a
   >>> referenced by drm_panel.c:100 (drivers/gpu/drm/drm_panel.c:100)
   >>>               drivers/gpu/drm/drm_panel.o:(drm_panel_remove) in archive vmlinux.a

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Hi Anusha,

kernel test robot noticed the following build errors:

[auto build test ERROR on c8ba07caaecc622a9922cda49f24790821af8a71]

url:    https://github.com/intel-lab-lkp/linux/commits/Anusha-Srivatsa/drm-panel-Add-new-helpers-for-refcounted-panel-allocatons/20250326-012651
base:   c8ba07caaecc622a9922cda49f24790821af8a71
patch link:    https://lore.kernel.org/r/20250325-b4-panel-refcounting-v1-3-4e2bf5d19c5d%40redhat.com
patch subject: [PATCH 3/5] drm/panel: get/put panel reference in drm_panel_add/remove()
config: xtensa-randconfig-001-20250326 (https://download.01.org/0day-ci/archive/20250326/202503260710.gDo7vXVR-lkp@intel.com/config)
compiler: xtensa-linux-gcc (GCC) 7.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250326/202503260710.gDo7vXVR-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202503260710.gDo7vXVR-lkp@intel.com/

All errors (new ones prefixed by >>, old ones prefixed by <<):

WARNING: modpost: missing MODULE_DESCRIPTION() in arch/xtensa/platforms/iss/simdisk.o
WARNING: modpost: missing MODULE_DESCRIPTION() in lib/slub_kunit.o
>> ERROR: modpost: "drm_panel_put" [drivers/gpu/drm/drm.ko] undefined!
>> ERROR: modpost: "drm_panel_get" [drivers/gpu/drm/drm.ko] undefined!

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki