[reactos] 03/03: [VBE] Check if DDC is supported before trying to read EDID

[Hervé Poussineau]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=08e9000496e4630b8f6c8…

commit 08e9000496e4630b8f6c848df03aebfd4d74c547
Author:     Hervé Poussineau <hpoussin(a)reactos.org>
AuthorDate: Sat May 29 21:37:03 2021 +0200
Commit:     Hervé Poussineau <hpoussin(a)reactos.org>
CommitDate: Sat Jun 5 23:38:05 2021 +0200

    [VBE] Check if DDC is supported before trying to read EDID
    
    Also set Edx to 0 when reading Edid, as per specification.
    
    CORE-16695
---
 win32ss/drivers/miniport/vbe/edid.c | 14 +++++++++++++-
 win32ss/drivers/videoprt/videoprt.c |  4 ----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/win32ss/drivers/miniport/vbe/edid.c b/win32ss/drivers/miniport/vbe/edid.c
index a9ebe35dbbf..cde4fc35754 100644
--- a/win32ss/drivers/miniport/vbe/edid.c
+++ b/win32ss/drivers/miniport/vbe/edid.c
@@ -184,6 +184,19 @@ VBEReadEdid(
 
    VideoPortDebugPrint(Trace, "VBEMP: VBEReadEdid() called\n");
 
+   /*
+    * Check if DDC1/DDC2 is supported
+    */
+   VideoPortZeroMemory(&BiosRegisters, sizeof(BiosRegisters));
+   BiosRegisters.Eax = VBE_DDC;
+   VBEDeviceExtension->Int10Interface.Int10CallBios(
+      VBEDeviceExtension->Int10Interface.Context,
+      &BiosRegisters);
+   if (VBE_GETRETURNCODE(BiosRegisters.Eax) != VBE_SUCCESS)
+      return FALSE;
+   if ((BiosRegisters.Ebx & 3) == 0)
+      return FALSE;
+
    /*
     * Directly read EDID information
     */
@@ -191,7 +204,6 @@ VBEReadEdid(
    BiosRegisters.Eax = VBE_DDC;
    BiosRegisters.Ebx = VBE_DDC_READ_EDID;
    BiosRegisters.Ecx = ChildIndex;
-   BiosRegisters.Edx = 1;
    BiosRegisters.Edi = VBEDeviceExtension->TrampolineMemoryOffset;
    BiosRegisters.SegEs = VBEDeviceExtension->TrampolineMemorySegment;
    VBEDeviceExtension->Int10Interface.Int10CallBios(
diff --git a/win32ss/drivers/videoprt/videoprt.c b/win32ss/drivers/videoprt/videoprt.c
index 5d4c54a3559..b57cff52594 100644
--- a/win32ss/drivers/videoprt/videoprt.c
+++ b/win32ss/drivers/videoprt/videoprt.c
@@ -1233,10 +1233,6 @@ VideoPortEnumerateChildren(
                 {
                     /* Mark it invalid */
                     ChildExtension->EdidValid = FALSE;
-                    // FIXME: the following break workarounds CORE-16695
-                    // but prevents graphic cards to return an invalid
-                    // EDID as first child, and a valid one as second child.
-                    break;
                 }
             }
         }