edid: add support for DisplayID extension (5k resolution)

The Detailed Timing Descriptor has only 12 bits to store the
resolution. This limits the guest to 4095 pixels.

This patch adds support for the DisplayID extension, that has 2 full
bytes for that purpose, thus allowing 5k resolutions and above.

Based-on: <20210303152948.59943-2-akihiko.odaki@gmail.com>
Signed-off-by: Konstantin Nazarov <mail@knazarov.com>
Message-Id: <20210315114639.91953-3-mail@knazarov.com>

[ kraxel: minor workflow tweaks ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20210427150824.638359-1-kraxel@redhat.com
Message-Id: <20210427150824.638359-9-kraxel@redhat.com>

2 files changed, 74 insertions, 6 deletions

diff --git a/hw/display/edid-generate.c b/hw/display/edid-generate.c
index bdd01571fc..f2b874d5e3 100644
--- a/hw/display/edid-generate.c
+++ b/hw/display/edid-generate.c
@@ -229,8 +229,8 @@ static void edid_desc_ranges(uint8_t *desc)
     desc[7] =  30;
     desc[8] = 160;
 
-    /* max dot clock (1200 MHz) */
-    desc[9] = 1200 / 10;
+    /* max dot clock (2550 MHz) */
+    desc[9] = 2550 / 10;
 
     /* no extended timing information */
     desc[10] = 0x01;
@@ -336,15 +336,61 @@ uint32_t qemu_edid_dpi_to_mm(uint32_t dpi, uint32_t res)
     return res * 254 / 10 / dpi;
 }
 
+static void init_displayid(uint8_t *did)
+{
+    did[0] = 0x70; /* display id extension */
+    did[1] = 0x13; /* version 1.3 */
+    did[2] = 4;    /* length */
+    did[3] = 0x03; /* product type (0x03 == standalone display device) */
+    edid_checksum(did + 1, did[2] + 4);
+}
+
+static void qemu_displayid_generate(uint8_t *did, uint32_t refresh_rate,
+                                    uint32_t xres, uint32_t yres,
+                                    uint32_t xmm, uint32_t ymm)
+{
+    Timings timings;
+    generate_timings(&timings, refresh_rate, xres, yres);
+
+    did[0] = 0x70; /* display id extension */
+    did[1] = 0x13; /* version 1.3 */
+    did[2] = 23;   /* length */
+    did[3] = 0x03; /* product type (0x03 == standalone display device) */
+
+    did[5] = 0x03; /* Detailed Timings Data Block */
+    did[6] = 0x00; /* revision */
+    did[7] = 0x14; /* block length */
+
+    did[8]  = timings.clock  & 0xff;
+    did[9]  = (timings.clock & 0xff00) >> 8;
+    did[10] = (timings.clock & 0xff0000) >> 16;
+
+    did[11] = 0x88; /* leave aspect ratio undefined */
+
+    stw_le_p(did + 12, 0xffff & (xres - 1));
+    stw_le_p(did + 14, 0xffff & (timings.xblank - 1));
+    stw_le_p(did + 16, 0xffff & (timings.xfront - 1));
+    stw_le_p(did + 18, 0xffff & (timings.xsync - 1));
+
+    stw_le_p(did + 20, 0xffff & (yres - 1));
+    stw_le_p(did + 22, 0xffff & (timings.yblank - 1));
+    stw_le_p(did + 24, 0xffff & (timings.yfront - 1));
+    stw_le_p(did + 26, 0xffff & (timings.ysync - 1));
+
+    edid_checksum(did + 1, did[2] + 4);
+}
+
 void qemu_edid_generate(uint8_t *edid, size_t size,
                         qemu_edid_info *info)
 {
     uint8_t *desc = edid + 54;
     uint8_t *xtra3 = NULL;
     uint8_t *dta = NULL;
+    uint8_t *did = NULL;
     uint32_t width_mm, height_mm;
     uint32_t refresh_rate = info->refresh_rate ? info->refresh_rate : 75000;
     uint32_t dpi = 100; /* if no width_mm/height_mm */
+    uint32_t large_screen = 0;
 
     /* =============== set defaults  =============== */
 
@@ -360,6 +406,9 @@ void qemu_edid_generate(uint8_t *edid, size_t size,
     if (!info->prefy) {
         info->prefy = 768;
     }
+    if (info->prefx >= 4096 || info->prefy >= 4096) {
+        large_screen = 1;
+    }
     if (info->width_mm && info->height_mm) {
         width_mm = info->width_mm;
         height_mm = info->height_mm;
@@ -377,6 +426,12 @@ void qemu_edid_generate(uint8_t *edid, size_t size,
         edid_ext_dta(dta);
     }
 
+    if (size >= 384 && large_screen) {
+        did = edid + 256;
+        edid[126]++;
+        init_displayid(did);
+    }
+
     /* =============== header information =============== */
 
     /* fixed */
@@ -441,9 +496,12 @@ void qemu_edid_generate(uint8_t *edid, size_t size,
 
     /* =============== descriptor blocks =============== */
 
-    edid_desc_timing(desc, refresh_rate, info->prefx, info->prefy,
-                     width_mm, height_mm);
-    desc = edid_desc_next(edid, dta, desc);
+    if (!large_screen) {
+        /* The DTD section has only 12 bits to store the resolution */
+        edid_desc_timing(desc, refresh_rate, info->prefx, info->prefy,
+                         width_mm, height_mm);
+        desc = edid_desc_next(edid, dta, desc);
+    }
 
     xtra3 = desc;
     edid_desc_xtra3_std(xtra3);
@@ -472,12 +530,22 @@ void qemu_edid_generate(uint8_t *edid, size_t size,
         desc = edid_desc_next(edid, dta, desc);
     }
 
+    /* =============== display id extensions =============== */
+
+    if (did && large_screen) {
+        qemu_displayid_generate(did, refresh_rate, info->prefx, info->prefy,
+                                width_mm, height_mm);
+    }
+
     /* =============== finish up =============== */
 
     edid_checksum(edid, 127);
     if (dta) {
         edid_checksum(dta, 127);
     }
+    if (did) {
+        edid_checksum(did, 127);
+    }
 }
 
 size_t qemu_edid_size(uint8_t *edid)
diff --git a/hw/display/vga-pci.c b/hw/display/vga-pci.c
index 48d29630ab..62fb5c38c1 100644
--- a/hw/display/vga-pci.c
+++ b/hw/display/vga-pci.c
@@ -49,7 +49,7 @@ struct PCIVGAState {
     qemu_edid_info edid_info;
     MemoryRegion mmio;
     MemoryRegion mrs[4];
-    uint8_t edid[256];
+    uint8_t edid[384];
 };
 
 #define TYPE_PCI_VGA "pci-vga"