From ad6935415681abff0707e96ad214f9d24ed9d3c3 Mon Sep 17 00:00:00 2001
From: mcc45tr <mcc45tr@gmail.com>
Date: Mon, 7 Sep 2026 21:53:55 +0300
Subject: [PATCH] drm/panel: expose Xiaomi Nabu panel revision

---
 .../sysfs-driver-panel-novatek-nt36523        |  12 ++
 drivers/gpu/drm/panel/panel-novatek-nt36523.c | 195 ++++++++++++++++++
 2 files changed, 207 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-driver-panel-novatek-nt36523

diff --git a/Documentation/ABI/testing/sysfs-driver-panel-novatek-nt36523 b/Documentation/ABI/testing/sysfs-driver-panel-novatek-nt36523
new file mode 100644
index 000000000..ddebc26cf
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-panel-novatek-nt36523
@@ -0,0 +1,12 @@
+What:		/sys/bus/mipi-dsi/devices/*/panel_revision
+Date:		September 2026
+Contact:	mcc45tr <mcc45tr@gmail.com>
+Description:
+		Read-only hardware revision of the internal display module on
+		Xiaomi Pad 5 (nabu). The value is detected from the panel lockdown
+		discriminator used by Xiaomi's downstream display and touchscreen
+		drivers. Qualcomm UEFI's detected panel configuration is preferred;
+		the panel lockdown registers are a fallback. Possible values are
+		"36-02-0b", "42-02-0a", and "unknown". The attribute is present
+		only for the Nabu panel.
+Users:		SENEMOS Nabu display color-profile integration
diff --git a/drivers/gpu/drm/panel/panel-novatek-nt36523.c b/drivers/gpu/drm/panel/panel-novatek-nt36523.c
index 07ae4f00e..3b349dacc 100644
--- a/drivers/gpu/drm/panel/panel-novatek-nt36523.c
+++ b/drivers/gpu/drm/panel/panel-novatek-nt36523.c
@@ -7,11 +7,14 @@
 
 #include <linux/backlight.h>
 #include <linux/delay.h>
+#include <linux/efi.h>
 #include <linux/gpio/consumer.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_graph.h>
 #include <linux/regulator/consumer.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
 
 #include <video/mipi_display.h>
 
@@ -22,12 +25,23 @@
 #include <drm/drm_panel.h>
 
 #define DSI_NUM_MIN 1
+#define NABU_PANEL_LOCKDOWN_LEN 8
+#define NABU_PANEL_REVISION_ATTEMPTS 3
+
+#define NABU_DISPLAY_EFI_GUID \
+	EFI_GUID(0x882f8c2b, 0x9646, 0x435f, 0x8d, 0xe5, 0xf2, 0x08, 0xff, 0x80, 0xc1, 0xbd)
 
 static bool expose_nabu_90hz;
 module_param(expose_nabu_90hz, bool, 0444);
 MODULE_PARM_DESC(expose_nabu_90hz,
 		 "Expose Xiaomi Nabu experimental 90 Hz mode");
 
+enum nabu_panel_revision {
+	NABU_PANEL_REVISION_UNKNOWN,
+	NABU_PANEL_REVISION_36_02_0B,
+	NABU_PANEL_REVISION_42_02_0A,
+};
+
 struct panel_info {
 	struct drm_panel panel;
 	struct mipi_dsi_device *dsi[2];
@@ -38,6 +52,9 @@ struct panel_info {
 	struct backlight_device *backlight;
 	struct regulator *vddio;
 	unsigned int refresh_rate;
+	enum nabu_panel_revision nabu_revision;
+	bool nabu_revision_read;
+	u8 nabu_revision_attempts;
 };
 
 struct panel_desc {
@@ -64,6 +81,91 @@ static inline struct panel_info *to_panel_info(struct drm_panel *panel)
 	return container_of(panel, struct panel_info, panel);
 }
 
+static const char *nt36523_nabu_revision_name(enum nabu_panel_revision revision)
+{
+	switch (revision) {
+	case NABU_PANEL_REVISION_36_02_0B:
+		return "36-02-0b";
+	case NABU_PANEL_REVISION_42_02_0A:
+		return "42-02-0a";
+	default:
+		return "unknown";
+	}
+}
+
+static ssize_t panel_revision_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct panel_info *pinfo = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%s\n",
+			  nt36523_nabu_revision_name(pinfo->nabu_revision));
+}
+static DEVICE_ATTR_RO(panel_revision);
+
+static struct attribute *nt36523_nabu_attrs[] = {
+	&dev_attr_panel_revision.attr,
+	NULL,
+};
+
+static const struct attribute_group nt36523_nabu_attr_group = {
+	.attrs = nt36523_nabu_attrs,
+};
+
+static int nt36523_set_nabu_revision_from_name(struct panel_info *pinfo,
+					       const char *name, size_t len)
+{
+	if (strnstr(name, "36_02_0b", len) ||
+	    strnstr(name, "36-02-0b", len))
+		pinfo->nabu_revision = NABU_PANEL_REVISION_36_02_0B;
+	else if (strnstr(name, "42_02_0a", len) ||
+		 strnstr(name, "42-02-0a", len))
+		pinfo->nabu_revision = NABU_PANEL_REVISION_42_02_0A;
+	else
+		return -ENODEV;
+
+	return 0;
+}
+
+static int nt36523_read_nabu_panel_revision_efi(struct panel_info *pinfo)
+{
+#if IS_ENABLED(CONFIG_EFI)
+	efi_guid_t guid = NABU_DISPLAY_EFI_GUID;
+	char config[128] = {};
+	unsigned long size = sizeof(config) - 1;
+	efi_status_t status;
+	int ret;
+
+	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE))
+		return -EOPNOTSUPP;
+
+	/*
+	 * Qualcomm's UEFI display driver already probes the physical panel and
+	 * records the selected Nabu configuration.  Prefer that immutable boot
+	 * result over sending vendor read commands while dual-DSI is running.
+	 */
+	status = efi.get_variable(L"DisplayPanelConfiguration", &guid, NULL,
+				  &size, config);
+	if (status == EFI_NOT_FOUND)
+		return -ENOENT;
+	if (status != EFI_SUCCESS)
+		return -EIO;
+	if (!size || size >= sizeof(config))
+		return -EOVERFLOW;
+
+	config[size] = '\0';
+	ret = nt36523_set_nabu_revision_from_name(pinfo, config, size);
+	if (!ret)
+		dev_info(pinfo->panel.dev,
+			 "detected Nabu panel revision %s from UEFI\n",
+			 nt36523_nabu_revision_name(pinfo->nabu_revision));
+
+	return ret;
+#else
+	return -EOPNOTSUPP;
+#endif
+}
+
 static int elish_boe_init_sequence(struct panel_info *pinfo)
 {
 	struct mipi_dsi_device *dsi0 = pinfo->dsi[0];
@@ -1257,6 +1359,72 @@ static void nt36523_reset(struct panel_info *pinfo)
 	usleep_range(12000, 13000);
 }
 
+static int nt36523_read_nabu_panel_revision(struct panel_info *pinfo)
+{
+	struct mipi_dsi_device *dsi0 = pinfo->dsi[0];
+	struct mipi_dsi_device *dsi1 = pinfo->dsi[1];
+	struct mipi_dsi_multi_context select_ctx = { .dsi = NULL };
+	struct mipi_dsi_multi_context restore_ctx = { .dsi = NULL };
+	u8 lockdown[NABU_PANEL_LOCKDOWN_LEN];
+	int i, link, ret = -EIO;
+
+	/*
+	 * Xiaomi's two Nabu panel variants expose an eight-byte lockdown block
+	 * on vendor page 0x22.  Match the downstream protocol exactly: select the
+	 * page in LP mode and read registers 0x01 through 0x08 individually.  A
+	 * bonded panel can return the block on either link, so use DSI1 only when
+	 * the primary link does not return a complete block.
+	 */
+	mipi_dsi_dual_dcs_write_seq_multi(&select_ctx, dsi0, dsi1, 0xff, 0x22);
+	if (select_ctx.accum_err) {
+		ret = select_ctx.accum_err;
+		goto restore_page;
+	}
+
+	for (link = 0; link < ARRAY_SIZE(pinfo->dsi); link++) {
+		for (i = 0; i < NABU_PANEL_LOCKDOWN_LEN; i++) {
+			ret = mipi_dsi_dcs_read(pinfo->dsi[link], i + 1,
+						&lockdown[i], sizeof(lockdown[i]));
+			if (ret != sizeof(lockdown[i])) {
+				if (ret >= 0)
+					ret = -EIO;
+				break;
+			}
+		}
+		if (i == NABU_PANEL_LOCKDOWN_LEN)
+			break;
+	}
+
+	if (link == ARRAY_SIZE(pinfo->dsi))
+		goto restore_page;
+
+	switch (lockdown[1]) {
+	case 0x36:
+		pinfo->nabu_revision = NABU_PANEL_REVISION_36_02_0B;
+		ret = 0;
+		break;
+	case 0x42:
+		pinfo->nabu_revision = NABU_PANEL_REVISION_42_02_0A;
+		ret = 0;
+		break;
+	default:
+		ret = -ENODEV;
+		break;
+	}
+
+restore_page:
+	mipi_dsi_dual_dcs_write_seq_multi(&restore_ctx, dsi0, dsi1, 0xff, 0x10);
+	if (!ret && restore_ctx.accum_err)
+		ret = restore_ctx.accum_err;
+
+	if (!ret)
+		dev_info(pinfo->panel.dev,
+			 "detected Nabu panel revision %s from DSI lockdown\n",
+			 nt36523_nabu_revision_name(pinfo->nabu_revision));
+
+	return ret;
+}
+
 static int nt36523_sync_pen_fps(struct panel_info *pinfo, bool panel_init)
 {
 	struct mipi_dsi_device *dsi0 = pinfo->dsi[0];
@@ -1353,6 +1521,19 @@ static int nt36523_prepare(struct drm_panel *panel)
 		return ret;
 	}
 
+	if (pinfo->desc == &nabu_csot_desc && !pinfo->nabu_revision_read &&
+	    pinfo->nabu_revision_attempts < NABU_PANEL_REVISION_ATTEMPTS) {
+		pinfo->nabu_revision_attempts++;
+		ret = nt36523_read_nabu_panel_revision(pinfo);
+		if (!ret)
+			pinfo->nabu_revision_read = true;
+		else
+			dev_warn_ratelimited(panel->dev,
+				 "could not identify Nabu panel revision over DSI (attempt %u/%u): %d\n",
+				 pinfo->nabu_revision_attempts,
+				 NABU_PANEL_REVISION_ATTEMPTS, ret);
+	}
+
 	if (pinfo->desc->sync_pen_fps) {
 		ret = nt36523_sync_pen_fps(pinfo, true);
 		if (ret < 0) {
@@ -1567,6 +1748,20 @@ static int nt36523_probe(struct mipi_dsi_device *dsi)
 
 	pinfo->dsi[0] = dsi;
 	mipi_dsi_set_drvdata(dsi, pinfo);
+	if (pinfo->desc == &nabu_csot_desc) {
+		ret = nt36523_read_nabu_panel_revision_efi(pinfo);
+		if (!ret)
+			pinfo->nabu_revision_read = true;
+		else
+			dev_dbg(dev,
+				"Nabu UEFI panel configuration unavailable: %d\n",
+				ret);
+
+		ret = devm_device_add_group(dev, &nt36523_nabu_attr_group);
+		if (ret)
+			return dev_err_probe(dev, ret,
+					     "failed to add Nabu panel attributes\n");
+	}
 
 	ret = of_drm_get_panel_orientation(dev->of_node, &pinfo->orientation);
 	if (ret < 0) {