dispserv_apple: read the EDID through the DCP on Apple Silicon

get_edid walked IODisplayConnect, which does not exist on Apple Silicon: the display stack moved to the DCP, a coprocessor with its own firmware that owns the link, so the op reported -1 there and the menu said "not available". The DCP does publish one DCPAVServiceProxy per connected display, and IOKit carries two unpublished functions to get at it - IOAVServiceCreateWithService() to bind a proxy and IOAVServiceCopyEDID() to ask the DCP for the block it read over DDC. That is the route BetterDisplay and Lunar take; there is no public equivalent. Used here as the fallback when the IODisplayConnect walk finds nothing, so PowerPC and Intel keep the published path and only Apple Silicon reaches this one. Unpublished means the symbols can be withdrawn, so they are resolved with dlsym rather than linked: a macOS that drops them leaves the pointers NULL, logs once and reports -1, instead of a binary that will not launch. It is plain C - CoreFoundation and IOKit only, no Objective-C - and every CF object it takes is released, including on the paths that find nothing. The proxies carry no CoreGraphics display ID, so the one for the display in use is found by reading each external candidate's EDID and matching the identity bytes (manufacturer 8-9, product 10-11, serial 12-15) against what CoreGraphics reports for that display: the same three-way match the IODisplayConnect path makes, done on the block itself. Embedded proxies are skipped, since the built-in panel has no EDID to read. When nothing matches but exactly one external display answered, that block is taken - with two, the guess would be unsafe and is not made. No Metal or Apple Silicon toolchain here: the function body was checked against stub CoreFoundation and IOKit declarations, and the MacOS lane is the compile gate.
2026-11-08 17:28:49 -10:00 · 2026-09-11 06:39:24 +02:00
1 parent a59bdfc438
commit c851c33286
@@ -45,6 +45,8 @@
 * IODisplayConnect services this walks do not exist (the display stack
 * moved to DCP) and Apple published no replacement, so the walk finds
 * nothing and the op reports -1 there. */
+#include <dlfcn.h>
+
 #include <IOKit/IOKitLib.h>
 #include <IOKit/graphics/IOGraphicsLib.h>
 /* RARCH_HAS_CGDISPLAYMODE_API is defined in cocoa_common.h.  The
@@ -708,6 +710,135 @@ static void apple_display_server_get_video_output_size(void *data,
 }

 #if TARGET_OS_OSX
+/* ---- Apple Silicon: the display coprocessor's copy ----
+ *
+ * On Apple Silicon the IODisplayConnect services the IOKit path below
+ * walks do not exist: the display stack moved to the DCP, a separate
+ * coprocessor with its own firmware that owns the link. What it does
+ * expose is one DCPAVServiceProxy per connected display, and IOKit
+ * carries two unpublished functions to get at it -
+ * IOAVServiceCreateWithService() to bind a proxy and
+ * IOAVServiceCopyEDID() to ask the DCP for the block it read over
+ * DDC. This is the route BetterDisplay and Lunar take; there is no
+ * public equivalent.
+ *
+ * Unpublished means the symbols can go away, so they are resolved at
+ * runtime rather than linked: a macOS that drops them leaves the
+ * pointers NULL and the menu says "not available" instead of the
+ * binary refusing to launch. Plain C throughout - no Objective-C is
+ * needed for any of it, only CoreFoundation and IOKit.
+ *
+ * The proxies are not labelled with a CoreGraphics display ID, so the
+ * one belonging to the display in use is found by reading each
+ * candidate's EDID and matching the identity bytes (manufacturer at
+ * 8-9, product at 10-11, serial at 12-15) against what CoreGraphics
+ * reports for that display. That is the same three-way match the
+ * IOKit path makes, done on the block itself. */
+typedef CFTypeRef IOAVServiceRef;
+typedef IOAVServiceRef (*apple_avservice_create_t)(CFAllocatorRef, io_service_t);
+typedef IOReturn (*apple_avservice_copy_edid_t)(IOAVServiceRef, CFDataRef*);
+
+/* The block a proxy reports, if it is a whole number of 128-byte
+ * blocks and at least one. Returns the length, or 0. */
+static size_t apple_dcp_service_edid(apple_avservice_copy_edid_t copy_edid,
+      IOAVServiceRef av, uint8_t *out, size_t max)
+{
+   CFDataRef edid = NULL;
+   size_t len     = 0;
+   if (copy_edid(av, &edid) != kIOReturnSuccess || !edid)
+      return 0;
+   len = (size_t)CFDataGetLength(edid);
+   if (len > max)
+      len = max;
+   len -= len % 128;
+   if (len >= 128)
+      memcpy(out, CFDataGetBytePtr(edid), len);
+   else
+      len = 0;
+   CFRelease(edid);
+   return len;
+}
+
+static int apple_dcp_get_edid(uint32_t vendor, uint32_t product,
+      uint32_t serial, uint8_t *out, size_t max)
+{
+   static apple_avservice_create_t    create_service;
+   static apple_avservice_copy_edid_t copy_edid;
+   static bool resolved;
+   io_iterator_t it = 0;
+   io_service_t svc;
+   int n            = -1;
+   int candidates   = 0;
+   int only_len     = 0;
+
+   if (!resolved)
+   {
+      resolved       = true;
+      create_service = (apple_avservice_create_t)
+         dlsym(RTLD_DEFAULT, "IOAVServiceCreateWithService");
+      copy_edid      = (apple_avservice_copy_edid_t)
+         dlsym(RTLD_DEFAULT, "IOAVServiceCopyEDID");
+      if (!create_service || !copy_edid)
+         RARCH_LOG("[Video] IOAVService is not available on this macOS;"
+               " the display's EDID cannot be read through the DCP.\n");
+   }
+   if (!create_service || !copy_edid)
+      return -1;
+
+   if (IOServiceGetMatchingServices(0,
+            IOServiceMatching("DCPAVServiceProxy"), &it) != KERN_SUCCESS)
+      return -1;
+
+   while ((svc = IOIteratorNext(it)))
+   {
+      /* Location is External on a connected display and Embedded on
+       * the built-in panel, which has no EDID to read */
+      CFStringRef location = (CFStringRef)IORegistryEntrySearchCFProperty(
+            svc, kIOServicePlane, CFSTR("Location"), kCFAllocatorDefault,
+            kIORegistryIterateRecursively);
+      bool external = location
+         && CFGetTypeID(location) == CFStringGetTypeID()
+         && CFStringCompare(location, CFSTR("External"), 0) == kCFCompareEqualTo;
+      if (location)
+         CFRelease(location);
+      if (external)
+      {
+         IOAVServiceRef av = create_service(kCFAllocatorDefault, svc);
+         if (av)
+         {
+            size_t len = apple_dcp_service_edid(copy_edid, av, out, max);
+            if (len)
+            {
+               uint32_t v  = ((uint32_t)out[8] << 8) | out[9];
+               uint32_t p  = out[10] | ((uint32_t)out[11] << 8);
+               uint32_t sn = out[12] | ((uint32_t)out[13] << 8)
+                           | ((uint32_t)out[14] << 16)
+                           | ((uint32_t)out[15] << 24);
+               candidates++;
+               only_len = (int)len;
+               /* the serial only separates two identical monitors,
+                * and only when both sides report one */
+               if (v == vendor && p == product
+                     && (!serial || !sn || sn == serial))
+                  n = (int)len;
+            }
+            CFRelease(av);
+         }
+      }
+      IOObjectRelease(svc);
+      if (n > 0)
+         break;
+   }
+   IOObjectRelease(it);
+
+   /* No identity match, but exactly one external display answered and
+    * out still holds its block: that is the display in use. A second
+    * one makes the guess unsafe, so it is not made. */
+   if (n < 0 && candidates == 1)
+      n = only_len;
+   return n;
+}
+
 /* The EDID of the display the RetroArch window is on. CoreGraphics
 * hands out the display's vendor, model and serial; the IODisplayConnect
 * service carrying the same three under kDisplayVendorID /
@@ -787,6 +918,10 @@ static int apple_display_server_get_edid(void *data, uint8_t *out, size_t max)
      IOObjectRelease(svc);
   }
   IOObjectRelease(it);
+
+   /* Apple Silicon has no IODisplayConnect; ask the DCP instead */
+   if (n < 0)
+      n = apple_dcp_get_edid(vendor, product, serial, out, max);
   return n;
 }
 #ifdef __clang__