[RFC] ARC: [plat-hsdk]: Increase SDIO CIU frequency to 50000000Hz

[Eugeniy Paltsev]

Increase SDIO CIU frequency from 12500000Hz to 50000000Hz by
switching from the default divisor value (div-by-8) to the
minimum possible value of the divisor (div-by-2) in HSDK platform
code.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
---
NOTE: This patch can possibly fix last issue with SD card initialization
fault.

 arch/arc/boot/dts/hsdk.dts    | 11 ++++++-----
 arch/arc/plat-hsdk/platform.c |  7 +++++++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/arc/boot/dts/hsdk.dts b/arch/arc/boot/dts/hsdk.dts
index 8adde1b..8f627c2 100644
--- a/arch/arc/boot/dts/hsdk.dts
+++ b/arch/arc/boot/dts/hsdk.dts
@@ -137,14 +137,15 @@
 			/*
 			 * DW sdio controller has external ciu clock divider
 			 * controlled via register in SDIO IP. Due to its
-			 * unexpected default value (it should devide by 1
-			 * but it devides by 8) SDIO IP uses wrong clock and
+			 * unexpected default value (it should divide by 1
+			 * but it divides by 8) SDIO IP uses wrong clock and
 			 * works unstable (see STAR 9001204800)
+			 * We switched to the minimum possible value of the
+			 * divisor (div-by-2) in HSDK platform code.
 			 * So add temporary fix and change clock frequency
-			 * from 100000000 to 12500000 Hz until we fix dw sdio
-			 * driver itself.
+			 * to 50000000 Hz until we fix dw sdio driver itself.
 			 */
-			clock-frequency = <12500000>;
+			clock-frequency = <50000000>;
 			#clock-cells = <0>;
 		};
 
diff --git a/arch/arc/plat-hsdk/platform.c b/arch/arc/plat-hsdk/platform.c
index 744e62e..f0cdb13 100644
--- a/arch/arc/plat-hsdk/platform.c
+++ b/arch/arc/plat-hsdk/platform.c
@@ -74,6 +74,10 @@ static void __init hsdk_set_cpu_freq_1ghz(void)
 		pr_err("Failed to setup CPU frequency to 1GHz!");
 }
 
+#define SDIO_BASE		(ARC_PERIPHERAL_BASE + 0xA000)
+#define SDIO_UHS_REG_EXT	(SDIO_BASE + 0x108)
+#define SDIO_UHS_REG_EXT_DIV_2	(2 << 30)
+
 static void __init hsdk_init_early(void)
 {
 	/*
@@ -89,6 +93,9 @@ static void __init hsdk_init_early(void)
 	/* Really apply settings made above */
 	writel(1, (void __iomem *) CREG_PAE_UPDATE);
 
+	/* Switch SDIO external ciu clock divider from div-by-8 to div-by-2 */
+	iowrite32(SDIO_UHS_REG_EXT_DIV_2, (void __iomem *) SDIO_UHS_REG_EXT);
+
 	/*
 	 * Setup CPU frequency to 1GHz.
 	 * TODO: remove it after smart hsdk pll driver will be introduced.
-- 
2.9.3