[edk2-platforms][PATCH 3/4] RPi3: add support for Compute Module 3.

["Andrei Warkentin" <andrey.warkentin@gmail.com>]

Mostly strings and documentation, but also fixes a dumb bug
I introduced when I added SD block write validation back
in RaspberryPiPkg (which broke eMMC support, even though
I could have tested it with a discrete eMMC media on regular
Pies)

Signed-off-by: Andrei Warkentin <andrey.warkentin@gmail.com>
---
 Platform/RaspberryPi/Drivers/ConfigDxe/ConfigDxeHii.uni |  8 ++++----
 Platform/RaspberryPi/Drivers/MmcDxe/MmcBlockIo.c        |  1 +
 Platform/RaspberryPi/RPi3/Readme.md                     | 19 ++++++++++++-------
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/Platform/RaspberryPi/Drivers/ConfigDxe/ConfigDxeHii.uni b/Platform/RaspberryPi/Drivers/ConfigDxe/ConfigDxeHii.uni
index 26d803f7..07660072 100644
--- a/Platform/RaspberryPi/Drivers/ConfigDxe/ConfigDxeHii.uni
+++ b/Platform/RaspberryPi/Drivers/ConfigDxe/ConfigDxeHii.uni
@@ -53,8 +53,8 @@
 #string STR_MMC_FORM_TITLE       #language en-US "SD/MMC Configuration"
 #string STR_MMC_FORM_SUBTITLE    #language en-US "Note: UEFI only, OS may override settings."
 
-#string STR_MMC_SD_PROMPT        #language en-US "uSD Routing"
-#string STR_MMC_SD_HELP          #language en-US "Choose host controller to drive uSD slot"
+#string STR_MMC_SD_PROMPT        #language en-US "uSD/eMMC Routing"
+#string STR_MMC_SD_HELP          #language en-US "Choose host controller to drive local flash storage"
 #string STR_MMC_SD_EMMC2         #language en-US "eMMC2 SDHCI"
 #string STR_MMC_SD_SDHOST        #language en-US "Broadcom SDHOST"
 #string STR_MMC_SD_ARASAN        #language en-US "Arasan SDHCI"
@@ -65,12 +65,12 @@
 #string STR_MMC_DISMULTI_Y       #language en-US "Single-block transfers"
 
 #string STR_MMC_FORCE1BIT_PROMPT #language en-US "uSD Max Bus Width"
-#string STR_MMC_FORCE1BIT_HELP   #language en-US "Tweak for bad media"
+#string STR_MMC_FORCE1BIT_HELP   #language en-US "Tweak for bad media (N/A for eMMC)"
 #string STR_MMC_FORCE1BIT_Y      #language en-US "1 Bit Mode"
 #string STR_MMC_FORCE1BIT_N      #language en-US "4 Bit Mode"
 
 #string STR_MMC_FORCEDS_PROMPT   #language en-US "uSD Force Default Speed"
-#string STR_MMC_FORCEDS_HELP     #language en-US "Tweak for bad media"
+#string STR_MMC_FORCEDS_HELP     #language en-US "Tweak for bad media (N/A for eMMC)"
 #string STR_MMC_FORCEDS_Y        #language en-US "Force Default Speed"
 #string STR_MMC_FORCEDS_N        #language en-US "Allow High Speed"
 
diff --git a/Platform/RaspberryPi/Drivers/MmcDxe/MmcBlockIo.c b/Platform/RaspberryPi/Drivers/MmcDxe/MmcBlockIo.c
index 29a9fd7d..8a2f7f42 100644
--- a/Platform/RaspberryPi/Drivers/MmcDxe/MmcBlockIo.c
+++ b/Platform/RaspberryPi/Drivers/MmcDxe/MmcBlockIo.c
@@ -47,6 +47,7 @@ ValidateWrittenBlockCount (
     /*
      * Not on MMC.
      */
+    *TransferredBlocks = Count;
     return EFI_SUCCESS;
   }
 
diff --git a/Platform/RaspberryPi/RPi3/Readme.md b/Platform/RaspberryPi/RPi3/Readme.md
index 3484c92c..b756013b 100644
--- a/Platform/RaspberryPi/RPi3/Readme.md
+++ b/Platform/RaspberryPi/RPi3/Readme.md
@@ -21,6 +21,10 @@ The RPi3 target supports Pi revisions based on the BCM2837 SoC:
 - Raspberry Pi 3A+
 - Raspberry Pi 3B
 - Raspberry Pi 3B+
+- Raspberry Pi CM3
+
+Note: a CM3L, lacking eMMC and thus similar to the 3B, will probably work as well, but just
+has not been tested.
 
 Please see the RPi4 target for BCM2711-based variants, such as the Raspberry Pi 4B.
 
@@ -148,20 +152,21 @@ This should allow you to set whatever date/time you want using the Shell date an
 time commands. While in UEFI or HLOS, the time will tick forward.
 `RtcEpochSeconds` is not updated on reboots.
 
-## uSD
+## uSD (and eMMC for CM3)
 
-UEFI supports both the Arasan SDHCI and the Broadcom SDHost controllers to access the uSD slot.
-You can use either. The other controller gets routed to the SDIO card. The choice made will
+UEFI supports both the Arasan SDHCI and the Broadcom SDHost controllers to access the flash
+media (eMMC on CM3, and uSD slot on everything else). You can use either. The other controller
+gets routed to the SDIO WiFi card (N/A to models without WiFi). The choice made will
 impact ACPI OSes booted (e.g. Windows 10). Arasan, being an SDIO controller, is usually used
-with the WiFi adapter where available. SDHost cannot be used with SDIO. In UEFI setup screen:
+with the WiFi adapter (where available). SDHost cannot be used with SDIO. In UEFI setup screen:
 - go to `Device Manager`
 - go to `Raspberry Pi Configuration`
-- go to `Chipset`
-- configure `Boot uSD Routing`
+- go to `SD/MMC Configuration`
+- configure `uSD/eMMC Routing`
 
 Known issues:
 - Arasan HS/4bit support is missing.
-- No 8 bit mode support for (e)MMC (irrelevant for the Pi 3).
+- No 8 bit mode support for (e)MMC (slow UEFI file I/O on CM3).
 - Hacky (e)MMC support (no HS).
 - No card removal/replacement detection, tons of timeouts and slow down during boot without an uSD card present.
 
-- 
2.17.1