[PATCH 3/4] EmbeddedPkg/DwEmmc: Fix DMA transfer length

[tien.hock.loh@intel.com]

From: "Loh, Tien Hock" <tien.hock.loh@intel.com>

DMA should not transfer more than requested length otherwise FIFO might run
into buffer underrun and causes errors in future transfers.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Loh Tien Hock <tien.hock.loh@intel.com>
---
 EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c b/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c
index 600ab01..c232309 100644
--- a/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c
+++ b/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c
@@ -496,7 +496,13 @@ PrepareDmaData (
 
   Cnt = (Length + DWEMMC_DMA_BUF_SIZE - 1) / DWEMMC_DMA_BUF_SIZE;
   Blks = (Length + DWEMMC_BLOCK_SIZE - 1) / DWEMMC_BLOCK_SIZE;
-  Length = DWEMMC_BLOCK_SIZE * Blks;
+
+  if(Length < DWEMMC_BLOCK_SIZE) {
+    Length = Length;
+  }
+  else {
+    Length = DWEMMC_BLOCK_SIZE * Blks;
+  }
 
   for (Idx = 0; Idx < Cnt; Idx++) {
     (IdmacDesc + Idx)->Des0 = DWEMMC_IDMAC_DES0_OWN | DWEMMC_IDMAC_DES0_CH |
@@ -534,11 +540,18 @@ StartDma (
   Data |= DWEMMC_CTRL_INT_EN | DWEMMC_CTRL_DMA_EN | DWEMMC_CTRL_IDMAC_EN;
   MmioWrite32 (DWEMMC_CTRL, Data);
   Data = MmioRead32 (DWEMMC_BMOD);
+
   Data |= DWEMMC_IDMAC_ENABLE | DWEMMC_IDMAC_FB;
   MmioWrite32 (DWEMMC_BMOD, Data);
 
-  MmioWrite32 (DWEMMC_BLKSIZ, DWEMMC_BLOCK_SIZE);
-  MmioWrite32 (DWEMMC_BYTCNT, Length);
+  if(Length < DWEMMC_BLOCK_SIZE) {
+    MmioWrite32 (DWEMMC_BLKSIZ, Length);
+    MmioWrite32 (DWEMMC_BYTCNT, Length);
+  }
+  else {
+    MmioWrite32 (DWEMMC_BLKSIZ, DWEMMC_BLOCK_SIZE);
+    MmioWrite32 (DWEMMC_BYTCNT, Length);
+  }
 }
 
 EFI_STATUS
-- 
2.2.2