From a01cd9c993cd0ee6df4cf6132e911051fe8664b8 Mon Sep 17 00:00:00 2001
From: Maxim Poliakovski <maximumspatium@googlemail.com>
Date: Tue, 9 Nov 2021 14:15:08 +0100
Subject: [PATCH] Make display ID method selectable in video controller.

---
 devices/video/atirage.cpp   |  2 +-
 devices/video/displayid.cpp | 16 +++++++---------
 devices/video/displayid.h   | 12 +++++++++---
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/devices/video/atirage.cpp b/devices/video/atirage.cpp
index 441b15b..73bfe09 100644
--- a/devices/video/atirage.cpp
+++ b/devices/video/atirage.cpp
@@ -120,7 +120,7 @@ ATIRage::ATIRage(uint16_t dev_id, uint32_t vmem_size_mb)
                     (asic_id << 24) | dev_id);
 
     /* initialize display identification */
-    this->disp_id = new DisplayID();
+    this->disp_id = new DisplayID(Disp_Id_Kind::DDC2B);
 }
 
 ATIRage::~ATIRage()
diff --git a/devices/video/displayid.cpp b/devices/video/displayid.cpp
index b9a81ee..3686c53 100644
--- a/devices/video/displayid.cpp
+++ b/devices/video/displayid.cpp
@@ -24,8 +24,10 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 #include <devices/video/displayid.h>
 #include <loguru.hpp>
 
-DisplayID::DisplayID()
+DisplayID::DisplayID(Disp_Id_Kind id_kind)
 {
+    this->id_kind = id_kind;
+
     /* Initialize Apple monitor codes */
     this->std_sense_code = 6;
     this->ext_sense_code = 0x2B;
@@ -37,9 +39,6 @@ DisplayID::DisplayID()
     this->last_scl   = 1;
     this->data_out   = 0x3000;
     this->data_ptr   = 0;
-
-    /* DDC sense mode is on by default */
-    this->i2c_on = true;
 }
 
 
@@ -70,18 +69,18 @@ uint16_t DisplayID::read_monitor_sense(uint16_t data, uint16_t dirs)
     uint16_t result;
 
     if ((dirs & 0x3100) == 0 && (data & 0x3100) == 0x3100) {
-        LOG_F(WARNING, "DisplayID: Hackish Monitor ID Switch activated!");
-        this->i2c_on = false;
+        LOG_F(WARNING, "DisplayID: Monitor sense lines tristated!");
     }
 
-    if (this->i2c_on) {
+    switch(this->id_kind) {
+    case Disp_Id_Kind::DDC2B:
         /* if GPIO pins are in the output mode, pick up their values
            In the input mode, GPIO pins will be read "high" */
         scl = (dirs & 0x1000) ? !!(data & 0x1000) : 1;
         sda = (dirs & 0x2000) ? !!(data & 0x2000) : 1;
 
         return update_ddc_i2c(sda, scl);
-    } else { /* Apple legacy monitor codes (see Technical Note HW30) */
+    case Disp_Id_Kind::AppleSense:
         switch (dirs & 0x3100) {
         case 0:
             result = ((this->std_sense_code & 6) << 11) | ((this->std_sense_code & 1) << 8);
@@ -98,7 +97,6 @@ uint16_t DisplayID::read_monitor_sense(uint16_t data, uint16_t dirs)
         default:
             result = 0x3100U;
         }
-
         return result;
     }
 }
diff --git a/devices/video/displayid.h b/devices/video/displayid.h
index 400d121..6fbf317 100644
--- a/devices/video/displayid.h
+++ b/devices/video/displayid.h
@@ -26,7 +26,7 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
     video cards.
 
     DisplayID provides two methods for display identification:
-    - Apple monitor sense codes as described in the Technical Note HW30
+    - Apple monitor sense as described in the Technical Note HW30
     - Display Data Channel (DDC) standardized by VESA
  */
 
@@ -35,6 +35,12 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 #include <cinttypes>
 
+/* Supported diplay ID methods. */
+enum class Disp_Id_Kind {
+    AppleSense,
+    DDC2B,
+};
+
 /** I2C bus states. */
 enum I2CState : uint8_t {
     STOP     = 0, /* transaction started           */
@@ -49,7 +55,7 @@ enum I2CState : uint8_t {
 
 class DisplayID {
 public:
-    DisplayID();
+    DisplayID(Disp_Id_Kind id_kind);
     ~DisplayID() = default;
 
     uint16_t read_monitor_sense(uint16_t data, uint16_t dirs);
@@ -59,7 +65,7 @@ protected:
     uint16_t update_ddc_i2c(uint8_t sda, uint8_t scl);
 
 private:
-    bool i2c_on;
+    Disp_Id_Kind    id_kind;
 
     uint8_t std_sense_code;
     uint8_t ext_sense_code;