[PATCH v2 1/1] drm/i915/gmbus: Add bit-banging debugfs control

[Naladala Ramanaidu <ramanaidu.naladala@intel.com>]

Add a connector debugfs interface to enable or disable I2C
bit-banging for Intel GMBUS adapters.

v1: Address below review comments: (Jani Nikula)
    - Remove HDMI-specific EDID read path changes.
    - Control bit-banging directly from debugfs via intel_gmbus_force_bit()

Assisted-by: OpenAI Codex:GPT-5
Signed-off-by: Naladala Ramanaidu <ramanaidu.naladala@intel.com>
---
 .../drm/i915/display/intel_display_debugfs.c  |  3 +
 .../drm/i915/display/intel_display_types.h    |  1 +
 drivers/gpu/drm/i915/display/intel_gmbus.c    | 61 +++++++++++++++++++
 drivers/gpu/drm/i915/display/intel_gmbus.h    |  3 +
 4 files changed, 68 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
index 3e302f23f247..74f065175a72 100644
--- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
+++ b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
@@ -40,6 +40,7 @@
 #include "intel_fb.h"
 #include "intel_fbc.h"
 #include "intel_fbdev.h"
+#include "intel_gmbus.h"
 #include "intel_hdcp.h"
 #include "intel_hdmi.h"
 #include "intel_hotplug.h"
@@ -1327,6 +1328,8 @@ void intel_connector_debugfs_add(struct intel_connector *connector)
 	if (!root)
 		return;
 
+	intel_gmbus_connector_debugfs_add(connector);
+
 	intel_drrs_connector_debugfs_add(connector);
 	intel_hdcp_connector_debugfs_add(connector);
 	intel_pps_connector_debugfs_add(connector);
diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 79f30660c2b6..5cef2582c361 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -558,6 +558,7 @@ struct intel_connector {
 	u8 polled;
 
 	int force_joined_pipes;
+	bool force_bit_banging;
 
 	struct {
 		struct drm_dp_aux *dsc_decompression_aux;
diff --git a/drivers/gpu/drm/i915/display/intel_gmbus.c b/drivers/gpu/drm/i915/display/intel_gmbus.c
index 60a70dea5d85..38d6d1148399 100644
--- a/drivers/gpu/drm/i915/display/intel_gmbus.c
+++ b/drivers/gpu/drm/i915/display/intel_gmbus.c
@@ -27,6 +27,7 @@
  *	Chris Wilson <chris@chris-wilson.co.uk>
  */
 
+#include <linux/debugfs.h>
 #include <linux/export.h>
 #include <linux/i2c-algo-bit.h>
 #include <linux/i2c.h>
@@ -871,6 +872,66 @@ static const struct i2c_algorithm gmbus_algorithm = {
 	.functionality	= gmbus_func
 };
 
+bool intel_gmbus_is_adapter(struct i2c_adapter *adapter)
+{
+	return adapter->algo == &gmbus_algorithm;
+}
+
+static int intel_force_bit_banging_show(struct seq_file *m, void *data)
+{
+	struct intel_connector *connector = m->private;
+
+	seq_printf(m, "%u\n", connector->force_bit_banging);
+
+	return 0;
+}
+
+static ssize_t intel_force_bit_banging_write(struct file *file,
+						     const char __user *ubuf,
+						     size_t len, loff_t *offp)
+{
+	struct seq_file *m = file->private_data;
+	struct intel_connector *connector = m->private;
+	bool force_bit_banging;
+	int ret;
+
+	ret = kstrtobool_from_user(ubuf, len, &force_bit_banging);
+	if (ret)
+		return ret;
+
+	if (force_bit_banging != connector->force_bit_banging) {
+		intel_gmbus_force_bit(connector->base.ddc, force_bit_banging);
+		connector->force_bit_banging = force_bit_banging;
+	}
+
+	*offp += len;
+
+	return len;
+}
+
+static int intel_force_bit_banging_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, intel_force_bit_banging_show, inode->i_private);
+}
+
+static const struct file_operations intel_force_bit_banging_fops = {
+	.owner = THIS_MODULE,
+	.open = intel_force_bit_banging_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+	.write = intel_force_bit_banging_write,
+};
+
+void intel_gmbus_connector_debugfs_add(struct intel_connector *connector)
+{
+	if (connector->base.ddc &&
+	    intel_gmbus_is_adapter(connector->base.ddc))
+		debugfs_create_file("intel_force_bit_banging", 0644,
+				    connector->base.debugfs_entry, connector,
+				    &intel_force_bit_banging_fops);
+}
+
 static void gmbus_lock_bus(struct i2c_adapter *adapter,
 			   unsigned int flags)
 {
diff --git a/drivers/gpu/drm/i915/display/intel_gmbus.h b/drivers/gpu/drm/i915/display/intel_gmbus.h
index 5fdeab1aa794..968f8cb42821 100644
--- a/drivers/gpu/drm/i915/display/intel_gmbus.h
+++ b/drivers/gpu/drm/i915/display/intel_gmbus.h
@@ -9,6 +9,7 @@
 #include <linux/types.h>
 
 struct i2c_adapter;
+struct intel_connector;
 struct intel_display;
 
 #define GMBUS_PIN_DISABLED	0
@@ -41,6 +42,8 @@ int intel_gmbus_output_aksv(struct i2c_adapter *adapter);
 
 struct i2c_adapter *
 intel_gmbus_get_adapter(struct intel_display *display, unsigned int pin);
+bool intel_gmbus_is_adapter(struct i2c_adapter *adapter);
+void intel_gmbus_connector_debugfs_add(struct intel_connector *connector);
 void intel_gmbus_force_bit(struct i2c_adapter *adapter, bool force_bit);
 bool intel_gmbus_is_forced_bit(struct i2c_adapter *adapter);
 void intel_gmbus_reset(struct intel_display *display);
-- 
2.43.0