From 33dadb270b4e72da565c6fcb0094916b1363cd03 Mon Sep 17 00:00:00 2001
From: snowpiaoling <1972997989@qq.com>
Date: Fri, 7 Aug 2026 12:30:07 +0800
Subject: [PATCH] EmbeddedPkg: normalize mmc interaction latency to 1us

Upon inspecting the source code, I found that the original implementation
of eMMC timeout in MmcDxe is affected by the CPU execution speed. With
higher-performance CPUs, the actual timeout duration would be shortened as
it was not based on wall clock.

Add a precise 1us delay to each iteration of the wait loop to make the
actual duration of the delay clock- and performance-agnostic.

Signed-off-by: snowpiaoling <1972997989@qq.com>
---
 EmbeddedPkg/Universal/MmcDxe/MmcBlockIo.c        | 4 ++++
 EmbeddedPkg/Universal/MmcDxe/MmcIdentification.c | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/EmbeddedPkg/Universal/MmcDxe/MmcBlockIo.c b/EmbeddedPkg/Universal/MmcDxe/MmcBlockIo.c
index 69987e9f1a..52908f92cf 100644
--- a/EmbeddedPkg/Universal/MmcDxe/MmcBlockIo.c
+++ b/EmbeddedPkg/Universal/MmcDxe/MmcBlockIo.c
@@ -210,6 +210,8 @@ MmcTransferBlock (
         break;  // Prevents delay once finished
       }
     }
+
+    gBS->Stall (1);
   }
 
   if (BufferSize > This->Media->BlockSize) {
@@ -323,6 +325,8 @@ MmcIoBlocks (
       if (!EFI_ERROR (Status)) {
         MmcHost->ReceiveResponse (MmcHost, MMC_RESPONSE_TYPE_R1, Response);
       }
+
+      gBS->Stall (1);
     }
 
     if (0 == Timeout) {
diff --git a/EmbeddedPkg/Universal/MmcDxe/MmcIdentification.c b/EmbeddedPkg/Universal/MmcDxe/MmcIdentification.c
index fed1646b27..858836cfc6 100755
--- a/EmbeddedPkg/Universal/MmcDxe/MmcIdentification.c
+++ b/EmbeddedPkg/Universal/MmcDxe/MmcIdentification.c
@@ -596,6 +596,10 @@ MmcIdentificationMode (
       return Status;
     }
 
+    if (!OcrResponse.Ocr.PowerUp) {
+      gBS->Stall (1);
+    }
+
     Timeout--;
   } while (!OcrResponse.Ocr.PowerUp && (Timeout > 0));