drm/i915/gmbus: Add Wa_16025573575 for PTL/WCL for bit-bashing

As per Wa_16025573575 for PTL/WCL, set the GPIO masks bit before starting
bit-bashing and maintain value through the bit-bashing sequence. After the
bit-bashing sequence is done, clear the GPIO masks bits.

v2:
-Use new helper for display workarounds. (Jani)
-Use a separate if-block for the workaround. (Gustavo)

v3:
-Document the workaround details in intel_display_wa.c
-Extend the workaround to WCL too. (Gustavo)

v4:
-Fix the platform check. (Gustavo)
-Avoid read when preserve bits are 0. (Gustavo)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20250715142211.3145299-1-ankit.k.nautiyal@intel.com

drivers/gpu/drm/i915/display/intel_display_wa.c

@@ -42,11 +42,23 @@ void intel_display_wa_apply(struct intel_display *display)
 		gen11_display_wa_apply(display);
 }
 
+/*
+ * Wa_16025573575:
+ * Fixes: Issue with bitbashing on Xe3 based platforms.
+ * Workaround: Set masks bits in GPIO CTL and preserve it during bitbashing sequence.
+ */
+static bool intel_display_needs_wa_16025573575(struct intel_display *display)
+{
+	return DISPLAY_VERx100(display) == 3000 || DISPLAY_VERx100(display) == 3002;
+}
+
 bool __intel_display_wa(struct intel_display *display, enum intel_display_wa wa, const char *name)
 {
 	switch (wa) {
 	case INTEL_DISPLAY_WA_16023588340:
 		return intel_display_needs_wa_16023588340(display);
+	case INTEL_DISPLAY_WA_16025573575:
+		return intel_display_needs_wa_16025573575(display);
 	default:
 		drm_WARN(display->drm, 1, "Missing Wa number: %s\n", name);
 		break;

drivers/gpu/drm/i915/display/intel_display_wa.h

@@ -23,6 +23,7 @@ bool intel_display_needs_wa_16023588340(struct intel_display *display);
 
 enum intel_display_wa {
 	INTEL_DISPLAY_WA_16023588340,
+	INTEL_DISPLAY_WA_16025573575,
 };
 
 bool __intel_display_wa(struct intel_display *display, enum intel_display_wa wa, const char *name);

drivers/gpu/drm/i915/display/intel_gmbus.c

@@ -39,6 +39,7 @@
 #include "intel_de.h"
 #include "intel_display_regs.h"
 #include "intel_display_types.h"
+#include "intel_display_wa.h"
 #include "intel_gmbus.h"
 #include "intel_gmbus_regs.h"
 
@@ -240,14 +241,20 @@ static void bxt_gmbus_clock_gating(struct intel_display *display,
 static u32 get_reserved(struct intel_gmbus *bus)
 {
 	struct intel_display *display = bus->display;
-	u32 reserved = 0;
+	u32 preserve_bits = 0;
+
+	if (display->platform.i830 || display->platform.i845g)
+		return 0;
 
 	/* On most chips, these bits must be preserved in software. */
-	if (!display->platform.i830 && !display->platform.i845g)
-		reserved = intel_de_read_notrace(display, bus->gpio_reg) &
-			(GPIO_DATA_PULLUP_DISABLE | GPIO_CLOCK_PULLUP_DISABLE);
+	preserve_bits |= GPIO_DATA_PULLUP_DISABLE | GPIO_CLOCK_PULLUP_DISABLE;
 
-	return reserved;
+	/* Wa_16025573575: the masks bits need to be preserved through out */
+	if (intel_display_wa(display, 16025573575))
+		preserve_bits |= GPIO_CLOCK_DIR_MASK | GPIO_CLOCK_VAL_MASK |
+				 GPIO_DATA_DIR_MASK | GPIO_DATA_VAL_MASK;
+
+	return intel_de_read_notrace(display, bus->gpio_reg) & preserve_bits;
 }
 
 static int get_clock(void *data)
@@ -308,6 +315,22 @@ static void set_data(void *data, int state_high)
 	intel_de_posting_read(display, bus->gpio_reg);
 }
 
+static void
+ptl_handle_mask_bits(struct intel_gmbus *bus, bool set)
+{
+	struct intel_display *display = bus->display;
+	u32 reg_val = intel_de_read_notrace(display, bus->gpio_reg);
+	u32 mask_bits = GPIO_CLOCK_DIR_MASK | GPIO_CLOCK_VAL_MASK |
+			GPIO_DATA_DIR_MASK | GPIO_DATA_VAL_MASK;
+	if (set)
+		reg_val |= mask_bits;
+	else
+		reg_val &= ~mask_bits;
+
+	intel_de_write_notrace(display, bus->gpio_reg, reg_val);
+	intel_de_posting_read(display, bus->gpio_reg);
+}
+
 static int
 intel_gpio_pre_xfer(struct i2c_adapter *adapter)
 {
@@ -319,6 +342,9 @@ intel_gpio_pre_xfer(struct i2c_adapter *adapter)
 	if (display->platform.pineview)
 		pnv_gmbus_clock_gating(display, false);
 
+	if (intel_display_wa(display, 16025573575))
+		ptl_handle_mask_bits(bus, true);
+
 	set_data(bus, 1);
 	set_clock(bus, 1);
 	udelay(I2C_RISEFALL_TIME);
@@ -336,6 +362,9 @@ intel_gpio_post_xfer(struct i2c_adapter *adapter)
 
 	if (display->platform.pineview)
 		pnv_gmbus_clock_gating(display, true);
+
+	if (intel_display_wa(display, 16025573575))
+		ptl_handle_mask_bits(bus, false);
 }
 
 static void