Implement read and write operations on SC_TOP_LEFT, SC_BOTTOM_RIGHT,
and SRC_SC_BOTTOM_RIGHT registers. These registers are also updated
when the src and/or dst clipping fields on DP_GUI_MASTER_CNTL are set
to default clipping.

Scissor clipping is used when rendering text in X.org. The r128 driver
sends host data much wider than is necessary to draw a glyph and cuts it
down to size using clipping before rendering. The actual clipping
implementation follows in a future patch.

This also includes a very minor refactor of the combined
default_sc_bottom_right field in the registers struct to
default_sc_bottom and default_sc_right. This was done to
stay consistent with the other scissor registers and prevent repeated
masking and extraction.

Signed-off-by: Chad Jablonski <chad@jablonski.xyz>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
---
 hw/display/ati.c      | 71 +++++++++++++++++++++++++++++++++++++++++--
 hw/display/ati_int.h  |  9 +++++-
 hw/display/ati_regs.h |  2 ++
 3 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/hw/display/ati.c b/hw/display/ati.c
index 2f919bcd22..bbae5455d0 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c
@@ -520,7 +520,32 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, unsigned int size)
         val |= s->regs.default_tile << 16;
         break;
     case DEFAULT_SC_BOTTOM_RIGHT:
-        val = s->regs.default_sc_bottom_right;
+        val = (s->regs.default_sc_bottom << 16) |
+              s->regs.default_sc_right;
+        break;
+    case SC_TOP:
+        val = s->regs.sc_top;
+        break;
+    case SC_LEFT:
+        val = s->regs.sc_left;
+        break;
+    case SC_BOTTOM:
+        val = s->regs.sc_bottom;
+        break;
+    case SC_RIGHT:
+        val = s->regs.sc_right;
+        break;
+    case SRC_SC_BOTTOM:
+        val = s->regs.src_sc_bottom;
+        break;
+    case SRC_SC_RIGHT:
+        val = s->regs.src_sc_right;
+        break;
+    case SC_TOP_LEFT:
+    case SC_BOTTOM_RIGHT:
+    case SRC_SC_BOTTOM_RIGHT:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "Read from write-only register 0x%x\n", (unsigned)addr);
         break;
     default:
         break;
@@ -881,6 +906,17 @@ static void ati_mm_write(void *opaque, hwaddr addr,
         /* DP_MIX fields */
         s->regs.dp_rop3 = (data & GMC_ROP3_MASK) >> 16;
         s->regs.dp_src_source = (data & GMC_SRC_SOURCE_MASK) >> 24;
+
+        if (!(data & GMC_SRC_CLIPPING)) {
+            s->regs.src_sc_right = s->regs.default_sc_right;
+            s->regs.src_sc_bottom = s->regs.default_sc_bottom;
+        }
+        if (!(data & GMC_DST_CLIPPING)) {
+            s->regs.sc_top = 0;
+            s->regs.sc_left = 0;
+            s->regs.sc_right = s->regs.default_sc_right;
+            s->regs.sc_bottom = s->regs.default_sc_bottom;
+        }
         break;
     case DST_WIDTH_X:
         s->regs.dst_x = data & 0x3fff;
@@ -960,7 +996,38 @@ static void ati_mm_write(void *opaque, hwaddr addr,
         }
         break;
     case DEFAULT_SC_BOTTOM_RIGHT:
-        s->regs.default_sc_bottom_right = data & 0x3fff3fff;
+        s->regs.default_sc_right = data & 0x3fff;
+        s->regs.default_sc_bottom = (data >> 16) & 0x3fff;
+        break;
+    case SC_TOP_LEFT:
+        s->regs.sc_left = data & 0x3fff;
+        s->regs.sc_top = (data >> 16) & 0x3fff;
+        break;
+    case SC_LEFT:
+        s->regs.sc_left = data & 0x3fff;
+        break;
+    case SC_TOP:
+        s->regs.sc_top = data & 0x3fff;
+        break;
+    case SC_BOTTOM_RIGHT:
+        s->regs.sc_right = data & 0x3fff;
+        s->regs.sc_bottom = (data >> 16) & 0x3fff;
+        break;
+    case SC_RIGHT:
+        s->regs.sc_right = data & 0x3fff;
+        break;
+    case SC_BOTTOM:
+        s->regs.sc_bottom = data & 0x3fff;
+        break;
+    case SRC_SC_BOTTOM_RIGHT:
+        s->regs.src_sc_right = data & 0x3fff;
+        s->regs.src_sc_bottom = (data >> 16) & 0x3fff;
+        break;
+    case SRC_SC_RIGHT:
+        s->regs.src_sc_right = data & 0x3fff;
+        break;
+    case SRC_SC_BOTTOM:
+        s->regs.src_sc_bottom = data & 0x3fff;
         break;
     default:
         break;
diff --git a/hw/display/ati_int.h b/hw/display/ati_int.h
index 59a1812034..d9ac8ee135 100644
--- a/hw/display/ati_int.h
+++ b/hw/display/ati_int.h
@@ -79,7 +79,6 @@ typedef struct ATIVGARegs {
     uint32_t default_offset;
     uint32_t default_pitch;
     uint32_t default_tile;
-    uint32_t default_sc_bottom_right;
     uint8_t dp_src_source;
     uint8_t dp_rop3;
     uint8_t dp_dst_datatype;
@@ -88,6 +87,14 @@ typedef struct ATIVGARegs {
     bool host_big_endian_en;
     bool byte_pix_order;
     bool conversion_temp;
+    uint16_t default_sc_bottom;
+    uint16_t default_sc_right;
+    uint16_t sc_top;
+    uint16_t sc_left;
+    uint16_t sc_bottom;
+    uint16_t sc_right;
+    uint16_t src_sc_bottom;
+    uint16_t src_sc_right;
 } ATIVGARegs;
 
 struct ATIVGAState {
diff --git a/hw/display/ati_regs.h b/hw/display/ati_regs.h
index fce9270635..9c638314f0 100644
--- a/hw/display/ati_regs.h
+++ b/hw/display/ati_regs.h
@@ -405,6 +405,8 @@
 #define GMC_SRC_DATATYPE_MASK                   0x00003000
 #define GMC_BYTE_PIX_ORDER                      0x00004000
 #define GMC_CONVERSION_TEMP                     0x00008000
+#define GMC_SRC_CLIPPING                        0x00000004
+#define GMC_DST_CLIPPING                        0x00000008
 #define GMC_BRUSH_SOLIDCOLOR                    0x000000d0
 #define GMC_SRC_DSTCOLOR                        0x00003000
 #define GMC_BYTE_ORDER_MSB_TO_LSB               0x00000000
-- 
2.51.2