[PATCH 1/4] Add bits for link_n_exended for DISPLAY >= 14

[Ankit Nautiyal]

LINK_N register has bits 31:24 for extended link N value used for
HDMI2.1 and for an alternate mode of operation of DP TG DDA
(Bspec:50488).

Add support for these extra bits.

For displays with version 14 or higher, the `PIPE_LINK_N1_EXTENDED_MASK`
(bits 31:24) is used to handle the extended link N bits.
For older platforms, the `DATA_LINK_M_N_MASK` (bits 23:0) is used to
handle the standard link N bits. This distinction ensures clarity and
maintains the semantics for platforms that support the extended bits.
In subsequent changes the logic is updated to conditionally apply the
extended link N bits.

v2: Drop extra link_n_ext member. (Jani)
v3: Avoid link_n_ext in set_m_n helper. (Jani)
v4: Rebase, and update commit message.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 18 ++++++++++++++++--
 drivers/gpu/drm/i915/i915_reg.h              |  2 ++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 3afb85fe8536..8fb0df388571 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -2583,14 +2583,22 @@ void intel_set_m_n(struct intel_display *display,
 		   i915_reg_t data_m_reg, i915_reg_t data_n_reg,
 		   i915_reg_t link_m_reg, i915_reg_t link_n_reg)
 {
+	u32 link_n = m_n->link_n;
+
 	intel_de_write(display, data_m_reg, TU_SIZE(m_n->tu) | m_n->data_m);
 	intel_de_write(display, data_n_reg, m_n->data_n);
 	intel_de_write(display, link_m_reg, m_n->link_m);
+
+	if (DISPLAY_VER(display) >= 14)
+		link_n &= ~PIPE_LINK_N1_EXTENDED_MASK;
+	else
+		link_n &= DATA_LINK_M_N_MASK;
+
 	/*
 	 * On BDW+ writing LINK_N arms the double buffered update
 	 * of all the M/N registers, so it must be written last.
 	 */
-	intel_de_write(display, link_n_reg, m_n->link_n);
+	intel_de_write(display, link_n_reg, link_n);
 }
 
 bool intel_cpu_transcoder_has_m2_n2(struct intel_display *display,
@@ -3279,7 +3287,13 @@ void intel_get_m_n(struct intel_display *display,
 		   i915_reg_t link_m_reg, i915_reg_t link_n_reg)
 {
 	m_n->link_m = intel_de_read(display, link_m_reg) & DATA_LINK_M_N_MASK;
-	m_n->link_n = intel_de_read(display, link_n_reg) & DATA_LINK_M_N_MASK;
+	m_n->link_n = intel_de_read(display, link_n_reg);
+
+	if (DISPLAY_VER(display) >= 14)
+		m_n->link_n &= ~PIPE_LINK_N1_EXTENDED_MASK;
+	else
+		m_n->link_n &= DATA_LINK_M_N_MASK;
+
 	m_n->data_m = intel_de_read(display, data_m_reg) & DATA_LINK_M_N_MASK;
 	m_n->data_n = intel_de_read(display, data_n_reg) & DATA_LINK_M_N_MASK;
 	m_n->tu = REG_FIELD_GET(TU_SIZE_MASK, intel_de_read(display, data_m_reg)) + 1;
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index c5064eebe063..a2054aced4f8 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1869,6 +1869,8 @@
 
 #define _PIPEA_LINK_N1		0x60044
 #define _PIPEB_LINK_N1		0x61044
+#define  PIPE_LINK_N1_EXTENDED_MASK	REG_GENMASK(31, 24)
+#define  PIPE_LINK_N1_EXTENDED(val)	REG_FIELD_PREP(PIPE_LINK_N1_EXTENDED_MASK, (val))
 #define PIPE_LINK_N1(dev_priv, tran) _MMIO_TRANS2(dev_priv, tran, _PIPEA_LINK_N1)
 
 #define _PIPEA_LINK_M2		0x60048
-- 
2.45.2