fix: enclose rounded preferred timings in EDID ranges

dev/check-edid.py

@@ -77,6 +77,8 @@ with tempfile.TemporaryDirectory(prefix='qemu-edid-probe-') as temporary:
         (144000, 60000, 1920, 1080, 144),
         (144000, 0, 1600, 900, 144),
         (0, 144000, 1920, 1080, 144),
+        (50000, 0, 1920, 1080, 50),
+        (255000, 0, 1280, 800, 255),
     ]:
         data = subprocess.check_output([str(directory / 'probe'), *map(str, (configured, frontend, width, height))])
         assert all(sum(data[offset:offset + 128]) % 256 == 0 for offset in range(0, len(data), 128)), 'invalid EDID checksum'
@@ -93,6 +95,6 @@ with tempfile.TemporaryDirectory(prefix='qemu-edid-probe-') as temporary:
         assert ranges[5] <= actual <= ranges[6], f'vertical range {ranges[5:7]} excludes {actual}'
         horizontal_khz = clock / (horizontal + hblank) / 1000
         assert ranges[7] <= horizontal_khz <= ranges[8], f'horizontal range {ranges[7:9]} excludes {horizontal_khz}'
-        if expected <= 75:
+        if configured == 0 and expected <= 75:
             assert ranges[5:9] == bytes((50, 125, 30, 160)), 'legacy monitor range changed'
         print(f'PASS configured={configured}, frontend={frontend}: {width}x{height}@{actual:.6f}, ranges={list(ranges[5:9])}')

docs/verification.md

@@ -112,7 +112,11 @@ The probe applies the tracked patch to four relevant source files in a temporary
 directory, compiles the actual EDID and virtio GPU generator functions with a
 small dependency harness, and decodes the result. It checks 60/75 Hz fallback,
 144 Hz configuration, a conflicting 60 Hz frontend request, resized dimensions,
-checksums and monitor ranges. At 1920×1080/144000 mHz the preferred timing is
+checksums and monitor ranges. It also checks the supported vertical-refresh
+boundaries: 1920×1080/50000 mHz and 1280×800/255000 mHz. Range endpoints
+use floor/ceiling of the encoded timing after pixel-clock rounding, so the
+49.998895 Hz lower-boundary timing is included by a 49 Hz minimum. Normal
+automatic 60/75 Hz cases retain the legacy 50–125 Hz range. At 1920×1080/144000 mHz the preferred timing is
 143.997231 Hz after EDID clock rounding. This is an advertised guest mode,
 not measured frame delivery or proof of a 144 Hz physical output.
 

patches/qemu-virtio-refresh-rate.patch

@@ -33,13 +33,13 @@
      for (output_idx = 0, node = g->conf.outputs;
 --- a/hw/display/edid-generate.c
 +++ b/hw/display/edid-generate.c
-@@ -220,17 +220,17 @@
+@@ -220,17 +220,20 @@
      desc[5 + len] = '\n';
  }
  
 -static void edid_desc_ranges(uint8_t *desc)
-+static void edid_desc_ranges(uint8_t *desc, uint32_t refresh_rate,
-+                             uint32_t horizontal_rate)
++static void edid_desc_ranges(uint8_t *desc, uint64_t clock,
++                             uint32_t htotal, uint32_t vtotal)
  {
      edid_desc_type(desc, 0xfd);
  
@@ -50,22 +50,25 @@
 -    /* horizontal (30 -> 160 kHz) */
 -    desc[7] =  30;
 -    desc[8] = 160;
-+    /* Preserve the legacy ranges and include the preferred mode. */
-+    desc[5] = 50;
-+    desc[6] = MIN(255, MAX(125, DIV_ROUND_UP(refresh_rate, 1000)));
++    /* Enclose the encoded timing after its 10 kHz pixel-clock rounding,
++     * while retaining legacy ranges whenever they already contain it. */
++    uint64_t vperiod = (uint64_t)htotal * vtotal;
++    uint64_t hperiod = (uint64_t)htotal * 1000;
++    desc[5] = MIN(50, clock / vperiod);
++    desc[6] = MIN(255, MAX(125, DIV_ROUND_UP(clock, vperiod)));
 +
-+    desc[7] = 30;
-+    desc[8] = MIN(255, MAX(160, DIV_ROUND_UP(horizontal_rate, 1000)));
++    desc[7] = MIN(30, clock / hperiod);
++    desc[8] = MIN(255, MAX(160, DIV_ROUND_UP(clock, hperiod)));
  
      /* max dot clock (2550 MHz) */
      desc[9] = 2550 / 10;
-@@ -513,7 +513,8 @@
+@@ -513,7 +516,8 @@
       * so dta descriptor offsets don't move any more.
       */
  
 -    edid_desc_ranges(desc);
-+    edid_desc_ranges(desc, refresh_rate,
-+                     timings.clock * 10000 / (info->prefx + timings.xblank));
++    edid_desc_ranges(desc, (uint64_t)timings.clock * 10000,
++                     info->prefx + timings.xblank, info->prefy + timings.yblank);
      desc = edid_desc_next(edid, dta, desc);
  
      if (desc && info->name) {