[PATCH v2 0/3] drm/display: simplify support for transparent DRM bridges

[PATCH v2 0/3] drm/display: simplify support for transparent DRM bridges

[Dmitry Baryshkov]

Supporting DP/USB-C can result in a chain of several transparent
bridges (PHY, redrivers, mux, etc). This results in drivers having
similar boilerplate code for such bridges.

Next, these drivers are susceptible to -EPROBE_DEFER loops: the next
bridge can either be probed from the bridge->attach callback, when it is
too late to return -EPROBE_DEFER, or from the probe() callback, when the
next bridge might not yet be available, because it depends on the
resources provided by the probing device.

Last, but not least, this results in the the internal knowledge of DRM
subsystem slowly diffusing into other subsystems, like PHY or USB/TYPEC.

To solve all these issues, define a separate DRM helper, which creates
separate aux device just for the bridge. During probe such aux device
doesn't result in the EPROBE_DEFER loops. Instead it allows the device
drivers to probe properly, according to the actual resource
dependencies. The bridge auxdevs are then probed when the next bridge
becomes available, sparing drivers from drm_bridge_attach() returning
-EPROBE_DEFER.

Proposed merge strategy: immutable branch with the drm commit, which is
then merged into PHY and USB subsystems together with the corresponding
patch.

Changes since v1:
 - Added EXPORT_SYMBOL_GPL / MODULE_LICENSE / etc. to drm_simple_bridge

Dmitry Baryshkov (3):
  drm/display: add transparent bridge helper
  phy: qcom: qmp-combo: switch to DRM_SIMPLE_BRIDGE
  usb: typec: nb7vpq904m: switch to DRM_SIMPLE_BRIDGE

 drivers/gpu/drm/display/Kconfig             |   9 ++
 drivers/gpu/drm/display/Makefile            |   2 +
 drivers/gpu/drm/display/drm_simple_bridge.c | 125 ++++++++++++++++++++
 drivers/phy/qualcomm/Kconfig                |   2 +-
 drivers/phy/qualcomm/phy-qcom-qmp-combo.c   |  44 +------
 drivers/usb/typec/mux/Kconfig               |   2 +-
 drivers/usb/typec/mux/nb7vpq904m.c          |  44 +------
 include/drm/display/drm_simple_bridge.h     |  19 +++
 8 files changed, 161 insertions(+), 86 deletions(-)
 create mode 100644 drivers/gpu/drm/display/drm_simple_bridge.c
 create mode 100644 include/drm/display/drm_simple_bridge.h

-- 
2.39.2

[PATCH v2 1/3] drm/display: add transparent bridge helper

[Dmitry Baryshkov]

Define a helper for creating simple transparent bridges which serve the
only purpose of linking devices into the bridge chain up to the last
bridge representing the connector. This is especially useful for
DP/USB-C bridge chains, which can span across several devices, but do
not require any additional functionality from the intermediate bridges.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
 drivers/gpu/drm/display/Kconfig             |   9 ++
 drivers/gpu/drm/display/Makefile            |   2 +
 drivers/gpu/drm/display/drm_simple_bridge.c | 125 ++++++++++++++++++++
 include/drm/display/drm_simple_bridge.h     |  19 +++
 4 files changed, 155 insertions(+)
 create mode 100644 drivers/gpu/drm/display/drm_simple_bridge.c
 create mode 100644 include/drm/display/drm_simple_bridge.h

diff --git a/drivers/gpu/drm/display/Kconfig b/drivers/gpu/drm/display/Kconfig
index 09712b88a5b8..a6132984b9e3 100644
--- a/drivers/gpu/drm/display/Kconfig
+++ b/drivers/gpu/drm/display/Kconfig
@@ -49,3 +49,12 @@ config DRM_DP_CEC
 
 	  Note: not all adapters support this feature, and even for those
 	  that do support this they often do not hook up the CEC pin.
+
+config DRM_SIMPLE_BRIDGE
+	tristate
+	depends on DRM
+	select AUXILIARY_BUS
+	select DRM_PANEL_BRIDGE
+	help
+	  Simple transparent bridge that is used by several drivers to build
+	  bridges chain.
diff --git a/drivers/gpu/drm/display/Makefile b/drivers/gpu/drm/display/Makefile
index 17ac4a1006a8..6e2b0d7f24b3 100644
--- a/drivers/gpu/drm/display/Makefile
+++ b/drivers/gpu/drm/display/Makefile
@@ -16,3 +16,5 @@ drm_display_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
 drm_display_helper-$(CONFIG_DRM_DP_CEC) += drm_dp_cec.o
 
 obj-$(CONFIG_DRM_DISPLAY_HELPER) += drm_display_helper.o
+
+obj-$(CONFIG_DRM_SIMPLE_BRIDGE) += drm_simple_bridge.o
diff --git a/drivers/gpu/drm/display/drm_simple_bridge.c b/drivers/gpu/drm/display/drm_simple_bridge.c
new file mode 100644
index 000000000000..94cdd927b708
--- /dev/null
+++ b/drivers/gpu/drm/display/drm_simple_bridge.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2023 Linaro Ltd.
+ *
+ * Author: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
+ */
+#include <linux/auxiliary_bus.h>
+#include <linux/module.h>
+
+#include <drm/drm_bridge.h>
+#include <drm/display/drm_simple_bridge.h>
+
+static DEFINE_IDA(simple_bridge_ida);
+
+static void drm_simple_bridge_release(struct device *dev)
+{
+	struct auxiliary_device *adev = to_auxiliary_dev(dev);
+
+	kfree(adev);
+}
+
+static void drm_simple_bridge_unregister_adev(void *_adev)
+{
+	struct auxiliary_device *adev = _adev;
+
+	auxiliary_device_delete(adev);
+	auxiliary_device_uninit(adev);
+}
+
+int drm_simple_bridge_register(struct device *parent)
+{
+	struct auxiliary_device *adev;
+	int ret;
+
+	adev = kzalloc(sizeof(*adev), GFP_KERNEL);
+	if (!adev)
+		return -ENOMEM;
+
+	ret = ida_alloc(&simple_bridge_ida, GFP_KERNEL);
+	if (ret < 0)
+		return ret;
+
+	adev->id = ret;
+	adev->name = "simple_bridge";
+	adev->dev.parent = parent;
+	adev->dev.of_node = parent->of_node;
+	adev->dev.release = drm_simple_bridge_release;
+
+	ret = auxiliary_device_init(adev);
+	if (ret) {
+		kfree(adev);
+		return ret;
+	}
+
+	ret = auxiliary_device_add(adev);
+	if (ret) {
+		auxiliary_device_uninit(adev);
+		return ret;
+	}
+
+	return devm_add_action_or_reset(parent, drm_simple_bridge_unregister_adev, adev);
+}
+EXPORT_SYMBOL_GPL(drm_simple_bridge_register);
+
+struct drm_simple_bridge_data {
+	struct drm_bridge bridge;
+	struct drm_bridge *next_bridge;
+	struct device *dev;
+};
+
+static int drm_simple_bridge_attach(struct drm_bridge *bridge,
+				    enum drm_bridge_attach_flags flags)
+{
+	struct drm_simple_bridge_data *data;
+
+	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
+		return -EINVAL;
+
+	data = container_of(bridge, struct drm_simple_bridge_data, bridge);
+
+	return drm_bridge_attach(bridge->encoder, data->next_bridge, bridge,
+				 DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+}
+
+static const struct drm_bridge_funcs drm_simple_bridge_funcs = {
+	.attach	= drm_simple_bridge_attach,
+};
+
+static int drm_simple_bridge_probe(struct auxiliary_device *auxdev,
+				   const struct auxiliary_device_id *id)
+{
+	struct drm_simple_bridge_data *data;
+
+	data = devm_kzalloc(&auxdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->dev = &auxdev->dev;
+	data->next_bridge = devm_drm_of_get_bridge(&auxdev->dev, auxdev->dev.of_node, 0, 0);
+	if (IS_ERR(data->next_bridge))
+		return dev_err_probe(&auxdev->dev, PTR_ERR(data->next_bridge),
+				     "failed to acquire drm_bridge\n");
+
+	data->bridge.funcs = &drm_simple_bridge_funcs;
+	data->bridge.of_node = data->dev->of_node;
+
+	return devm_drm_bridge_add(data->dev, &data->bridge);
+}
+
+static const struct auxiliary_device_id drm_simple_bridge_table[] = {
+	{ .name = KBUILD_MODNAME ".simple_bridge" },
+	{},
+};
+MODULE_DEVICE_TABLE(auxiliary, drm_simple_bridge_table);
+
+struct auxiliary_driver drm_simple_bridge_drv = {
+	.name = "simple_bridge",
+	.id_table = drm_simple_bridge_table,
+	.probe = drm_simple_bridge_probe,
+};
+module_auxiliary_driver(drm_simple_bridge_drv);
+
+MODULE_AUTHOR("Dmitry Baryshkov <dmitry.baryshkov@linaro.org>");
+MODULE_DESCRIPTION("DRM simple bridge helper");
+MODULE_LICENSE("GPL");
diff --git a/include/drm/display/drm_simple_bridge.h b/include/drm/display/drm_simple_bridge.h
new file mode 100644
index 000000000000..3da8e1fb1137
--- /dev/null
+++ b/include/drm/display/drm_simple_bridge.h
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2023 Linaro Ltd.
+ *
+ * Author: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
+ */
+#ifndef DRM_SIMPLE_BRIDGE_H
+#define DRM_SIMPLE_BRIDGE_H
+
+#if IS_ENABLED(CONFIG_DRM_SIMPLE_BRIDGE)
+int drm_simple_bridge_register(struct device *parent);
+#else
+static inline int drm_simple_bridge_register(struct device *parent)
+{
+	return 0;
+}
+#endif
+
+#endif
-- 
2.39.2

[PATCH v2 2/3] phy: qcom: qmp-combo: switch to DRM_SIMPLE_BRIDGE

[Dmitry Baryshkov]

Switch to using the new DRM_SIMPLE_BRIDGE helper to create the
transparent DRM bridge device instead of handcoding corresponding
functionality.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
 drivers/phy/qualcomm/Kconfig              |  2 +-
 drivers/phy/qualcomm/phy-qcom-qmp-combo.c | 44 ++---------------------
 2 files changed, 3 insertions(+), 43 deletions(-)

diff --git a/drivers/phy/qualcomm/Kconfig b/drivers/phy/qualcomm/Kconfig
index ced603806375..fb03e3b3f637 100644
--- a/drivers/phy/qualcomm/Kconfig
+++ b/drivers/phy/qualcomm/Kconfig
@@ -63,7 +63,7 @@ config PHY_QCOM_QMP_COMBO
 	depends on DRM || DRM=n
 	select GENERIC_PHY
 	select MFD_SYSCON
-	select DRM_PANEL_BRIDGE if DRM
+	select DRM_SIMPLE_BRIDGE if DRM
 	help
 	  Enable this to support the QMP Combo PHY transceiver that is used
 	  with USB3 and DisplayPort controllers on Qualcomm chips.
diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
index 1793d49bf45c..4bf64899cc71 100644
--- a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
+++ b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
@@ -21,7 +21,7 @@
 #include <linux/usb/typec.h>
 #include <linux/usb/typec_mux.h>
 
-#include <drm/drm_bridge.h>
+#include <drm/display/drm_simple_bridge.h>
 
 #include <dt-bindings/phy/phy-qcom-qmp.h>
 
@@ -1419,8 +1419,6 @@ struct qmp_combo {
 	struct clk_hw dp_link_hw;
 	struct clk_hw dp_pixel_hw;
 
-	struct drm_bridge bridge;
-
 	struct typec_switch_dev *sw;
 	enum typec_orientation orientation;
 };
@@ -3193,44 +3191,6 @@ static int qmp_combo_typec_switch_register(struct qmp_combo *qmp)
 }
 #endif
 
-#if IS_ENABLED(CONFIG_DRM)
-static int qmp_combo_bridge_attach(struct drm_bridge *bridge,
-				   enum drm_bridge_attach_flags flags)
-{
-	struct qmp_combo *qmp = container_of(bridge, struct qmp_combo, bridge);
-	struct drm_bridge *next_bridge;
-
-	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
-		return -EINVAL;
-
-	next_bridge = devm_drm_of_get_bridge(qmp->dev, qmp->dev->of_node, 0, 0);
-	if (IS_ERR(next_bridge)) {
-		dev_err(qmp->dev, "failed to acquire drm_bridge: %pe\n", next_bridge);
-		return PTR_ERR(next_bridge);
-	}
-
-	return drm_bridge_attach(bridge->encoder, next_bridge, bridge,
-				 DRM_BRIDGE_ATTACH_NO_CONNECTOR);
-}
-
-static const struct drm_bridge_funcs qmp_combo_bridge_funcs = {
-	.attach	= qmp_combo_bridge_attach,
-};
-
-static int qmp_combo_dp_register_bridge(struct qmp_combo *qmp)
-{
-	qmp->bridge.funcs = &qmp_combo_bridge_funcs;
-	qmp->bridge.of_node = qmp->dev->of_node;
-
-	return devm_drm_bridge_add(qmp->dev, &qmp->bridge);
-}
-#else
-static int qmp_combo_dp_register_bridge(struct qmp_combo *qmp)
-{
-	return 0;
-}
-#endif
-
 static int qmp_combo_parse_dt_lecacy_dp(struct qmp_combo *qmp, struct device_node *np)
 {
 	struct device *dev = qmp->dev;
@@ -3436,7 +3396,7 @@ static int qmp_combo_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	ret = qmp_combo_dp_register_bridge(qmp);
+	ret = drm_simple_bridge_register(dev);
 	if (ret)
 		return ret;
 
-- 
2.39.2

[PATCH v2 3/3] usb: typec: nb7vpq904m: switch to DRM_SIMPLE_BRIDGE

[Dmitry Baryshkov]

Switch to using the new DRM_SIMPLE_BRIDGE helper to create the
transparent DRM bridge device instead of handcoding corresponding
functionality.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
 drivers/usb/typec/mux/Kconfig      |  2 +-
 drivers/usb/typec/mux/nb7vpq904m.c | 44 ++----------------------------
 2 files changed, 3 insertions(+), 43 deletions(-)

diff --git a/drivers/usb/typec/mux/Kconfig b/drivers/usb/typec/mux/Kconfig
index 784b9d8107e9..350a7ffce67e 100644
--- a/drivers/usb/typec/mux/Kconfig
+++ b/drivers/usb/typec/mux/Kconfig
@@ -39,7 +39,7 @@ config TYPEC_MUX_NB7VPQ904M
 	tristate "On Semiconductor NB7VPQ904M Type-C redriver driver"
 	depends on I2C
 	depends on DRM || DRM=n
-	select DRM_PANEL_BRIDGE if DRM
+	select DRM_SIMPLE_BRIDGE if DRM
 	select REGMAP_I2C
 	help
 	  Say Y or M if your system has a On Semiconductor NB7VPQ904M Type-C
diff --git a/drivers/usb/typec/mux/nb7vpq904m.c b/drivers/usb/typec/mux/nb7vpq904m.c
index 9360b65e8b06..c89a956412ea 100644
--- a/drivers/usb/typec/mux/nb7vpq904m.c
+++ b/drivers/usb/typec/mux/nb7vpq904m.c
@@ -11,7 +11,7 @@
 #include <linux/regmap.h>
 #include <linux/bitfield.h>
 #include <linux/of_graph.h>
-#include <drm/drm_bridge.h>
+#include <drm/display/drm_simple_bridge.h>
 #include <linux/usb/typec_dp.h>
 #include <linux/usb/typec_mux.h>
 #include <linux/usb/typec_retimer.h>
@@ -70,8 +70,6 @@ struct nb7vpq904m {
 	bool swap_data_lanes;
 	struct typec_switch *typec_switch;
 
-	struct drm_bridge bridge;
-
 	struct mutex lock; /* protect non-concurrent retimer & switch */
 
 	enum typec_orientation orientation;
@@ -297,44 +295,6 @@ static int nb7vpq904m_retimer_set(struct typec_retimer *retimer, struct typec_re
 	return ret;
 }
 
-#if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_DRM_PANEL_BRIDGE)
-static int nb7vpq904m_bridge_attach(struct drm_bridge *bridge,
-				    enum drm_bridge_attach_flags flags)
-{
-	struct nb7vpq904m *nb7 = container_of(bridge, struct nb7vpq904m, bridge);
-	struct drm_bridge *next_bridge;
-
-	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
-		return -EINVAL;
-
-	next_bridge = devm_drm_of_get_bridge(&nb7->client->dev, nb7->client->dev.of_node, 0, 0);
-	if (IS_ERR(next_bridge)) {
-		dev_err(&nb7->client->dev, "failed to acquire drm_bridge: %pe\n", next_bridge);
-		return PTR_ERR(next_bridge);
-	}
-
-	return drm_bridge_attach(bridge->encoder, next_bridge, bridge,
-				 DRM_BRIDGE_ATTACH_NO_CONNECTOR);
-}
-
-static const struct drm_bridge_funcs nb7vpq904m_bridge_funcs = {
-	.attach	= nb7vpq904m_bridge_attach,
-};
-
-static int nb7vpq904m_register_bridge(struct nb7vpq904m *nb7)
-{
-	nb7->bridge.funcs = &nb7vpq904m_bridge_funcs;
-	nb7->bridge.of_node = nb7->client->dev.of_node;
-
-	return devm_drm_bridge_add(&nb7->client->dev, &nb7->bridge);
-}
-#else
-static int nb7vpq904m_register_bridge(struct nb7vpq904m *nb7)
-{
-	return 0;
-}
-#endif
-
 static const struct regmap_config nb7_regmap = {
 	.max_register = 0x1f,
 	.reg_bits = 8,
@@ -461,7 +421,7 @@ static int nb7vpq904m_probe(struct i2c_client *client)
 
 	gpiod_set_value(nb7->enable_gpio, 1);
 
-	ret = nb7vpq904m_register_bridge(nb7);
+	ret = drm_simple_bridge_register(dev);
 	if (ret)
 		return ret;
 
-- 
2.39.2

Re: [PATCH v2 3/3] usb: typec: nb7vpq904m: switch to DRM_SIMPLE_BRIDGE

[kernel test robot]

Hi Dmitry,

kernel test robot noticed the following build errors:

[auto build test ERROR on drm-misc/drm-misc-next]
[also build test ERROR on usb/usb-testing usb/usb-next usb/usb-linus drm-intel/for-linux-next-fixes drm-tip/drm-tip linus/master v6.5-rc4 next-20230731]
[cannot apply to drm-intel/for-linux-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Dmitry-Baryshkov/drm-display-add-transparent-bridge-helper/20230731-152746
base:   git://anongit.freedesktop.org/drm/drm-misc drm-misc-next
patch link:    https://lore.kernel.org/r/20230731071930.3928150-4-dmitry.baryshkov%40linaro.org
patch subject: [PATCH v2 3/3] usb: typec: nb7vpq904m: switch to DRM_SIMPLE_BRIDGE
config: xtensa-randconfig-r004-20230731 (https://download.01.org/0day-ci/archive/20230731/202307311724.2bAqJu6o-lkp@intel.com/config)
compiler: xtensa-linux-gcc (GCC) 12.3.0
reproduce: (https://download.01.org/0day-ci/archive/20230731/202307311724.2bAqJu6o-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/202307311724.2bAqJu6o-lkp@intel.com/

All errors (new ones prefixed by >>):

   drivers/gpu/drm/display/drm_simple_bridge.c: In function 'drm_simple_bridge_probe':
>> drivers/gpu/drm/display/drm_simple_bridge.c:105:21: error: 'struct drm_bridge' has no member named 'of_node'
     105 |         data->bridge.of_node = data->dev->of_node;
         |                     ^


vim +105 drivers/gpu/drm/display/drm_simple_bridge.c

1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   88  
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   89  static int drm_simple_bridge_probe(struct auxiliary_device *auxdev,
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   90  				   const struct auxiliary_device_id *id)
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   91  {
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   92  	struct drm_simple_bridge_data *data;
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   93  
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   94  	data = devm_kzalloc(&auxdev->dev, sizeof(*data), GFP_KERNEL);
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   95  	if (!data)
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   96  		return -ENOMEM;
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   97  
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   98  	data->dev = &auxdev->dev;
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31   99  	data->next_bridge = devm_drm_of_get_bridge(&auxdev->dev, auxdev->dev.of_node, 0, 0);
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  100  	if (IS_ERR(data->next_bridge))
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  101  		return dev_err_probe(&auxdev->dev, PTR_ERR(data->next_bridge),
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  102  				     "failed to acquire drm_bridge\n");
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  103  
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  104  	data->bridge.funcs = &drm_simple_bridge_funcs;
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31 @105  	data->bridge.of_node = data->dev->of_node;
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  106  
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  107  	return devm_drm_bridge_add(data->dev, &data->bridge);
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  108  }
1b4ddd588d7e97 Dmitry Baryshkov 2023-07-31  109  

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