Re: [PATCH] drm/bridge: Select DRM_KMS_HELPER for DRM_PANEL_BRIDGE

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Hi Luca,

On 11/01/2024 13:38, Luca Weiss wrote:
Since the kconfig symbol of DRM_PANEL_BRIDGE is only adding
bridge/panel.o to drm_kms_helper object, we need to select
DRM_KMS_HELPER to make sure the file is actually getting built.

Otherwise with certain defconfigs e.g. devm_drm_of_get_bridge will not
be properly available:

   aarch64-linux-gnu-ld: drivers/phy/qualcomm/phy-qcom-qmp-combo.o: in function `qmp_combo_bridge_attach':
   drivers/phy/qualcomm/phy-qcom-qmp-combo.c:3204:(.text+0x8f4): undefined reference to `devm_drm_of_get_bridge'

Signed-off-by: Luca Weiss <luca.weiss@xxxxxxxxxxxxx>
---
I can see "depends on DRM_KMS_HELPER" was removed with commit
3c3384050d68 ("drm: Don't make DRM_PANEL_BRIDGE dependent on DRM_KMS_HELPERS")

I'm not too familiar with Kconfig but it feels more correct if
PHY_QCOM_QMP_COMBO selects DRM_PANEL_BRIDGE that that's enough; and it
doesn't also has to explicitly select DRM_KMS_HELPER because of how the
objects are built in the Makefile.

Alternatively solution to this patch could be adjusting this line in
include/drm/drm_bridge.h:

   -#if defined(CONFIG_OF) && defined(CONFIG_DRM_PANEL_BRIDGE)
   +#if defined(CONFIG_OF) && defined(CONFIG_DRM_PANEL_BRIDGE) && defined(CONFIG_DRM_KMS_HELPER)
    struct drm_bridge *devm_drm_of_get_bridge(struct device *dev, struct device_node *node,
                                             u32 port, u32 endpoint);

.. and then selecting DRM_KMS_HELPER for PHY_QCOM_QMP_COMBO.

But I think the solution in this patch is better. Let me know what you
think.

I think this is no more the case after on linux-next:
35921910bbd0 phy: qcom: qmp-combo: switch to DRM_AUX_BRIDGE

But could you still check ?

Neil

---
  drivers/gpu/drm/bridge/Kconfig | 1 +
  1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index ac9ec5073619..ae782b427829 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -8,6 +8,7 @@ config DRM_BRIDGE
  config DRM_PANEL_BRIDGE
  	def_bool y
  	depends on DRM_BRIDGE
+	select DRM_KMS_HELPER
  	select DRM_PANEL
  	help
  	  DRM bridge wrapper of DRM panels

---
base-commit: b9c3a1fa6fb324e691a03cf124b79f4842e65d76
change-id: 20240111-drm-panel-bridge-fixup-5c2977fb969f

Best regards,




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