From 5c8479b7e82155eed9e86658935dda7bf8202b8d Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Mon, 4 Jan 2016 14:42:17 +0000
Subject: [PATCH] BCM270X_DT: Add the sdtweak overlay, for tuning sdhost

The sdhost overlay declares the sdhost interface and allows parameters
to be set. This is overkill for situations where the user just wants to
tweak the parameters of a pre-declared sdhost interface, so create an
sdtweak overlay that does just that.
---
 arch/arm/boot/dts/overlays/Makefile            |  1 +
 arch/arm/boot/dts/overlays/README              | 14 ++++++++++++++
 arch/arm/boot/dts/overlays/sdtweak-overlay.dts | 21 +++++++++++++++++++++
 3 files changed, 36 insertions(+)
 create mode 100644 arch/arm/boot/dts/overlays/sdtweak-overlay.dts

--- a/arch/arm/boot/dts/overlays/Makefile
+++ b/arch/arm/boot/dts/overlays/Makefile
@@ -53,6 +53,7 @@ dtb-$(RPI_DT_OVERLAYS) += rpi-proto-over
 dtb-$(RPI_DT_OVERLAYS) += rpi-sense-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += sdhost-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += sdio-overlay.dtb
+dtb-$(RPI_DT_OVERLAYS) += sdtweak-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += smi-dev-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += smi-nand-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += smi-overlay.dtb
--- a/arch/arm/boot/dts/overlays/README
+++ b/arch/arm/boot/dts/overlays/README
@@ -635,6 +635,20 @@ Params: overclock_50             Clock (
                                  (default on: polling once at boot-time)
 
 
+Name:   sdtweak
+Info:   Tunes the bcm2835-sdhost SD/MMC driver
+Load:   dtoverlay=sdtweak,<param>=<val>
+Params: overclock_50             Clock (in MHz) to use when the MMC framework
+                                 requests 50MHz
+
+        force_pio                Disable DMA support (default off)
+
+        pio_limit                Number of blocks above which to use DMA
+                                 (default 1)
+
+        debug                    Enable debug output (default off)
+
+
 Name:   smi
 Info:   Enables the Secondary Memory Interface peripheral. Uses GPIOs 2-25!
 Load:   dtoverlay=smi
--- /dev/null
+++ b/arch/arm/boot/dts/overlays/sdtweak-overlay.dts
@@ -0,0 +1,21 @@
+/dts-v1/;
+/plugin/;
+
+/{
+	compatible = "brcm,bcm2708";
+
+	fragment@0 {
+		target = <&sdhost>;
+		frag1: __overlay__ {
+			brcm,overclock-50 = <0>;
+			brcm,pio-limit = <1>;
+		};
+	};
+
+	__overrides__ {
+		overclock_50     = <&frag1>,"brcm,overclock-50:0";
+		force_pio        = <&frag1>,"brcm,force-pio?";
+		pio_limit        = <&frag1>,"brcm,pio-limit:0";
+		debug            = <&frag1>,"brcm,debug?";
+	};
+};