linux-kernel - [PATCH] ARC: HSDK: DTS: Temporary fix of sdio ciu frequency

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Message-Id: <20170908184233.1779-1-Eugeniy.Paltsev@synopsys.com>
Date:   Fri,  8 Sep 2017 21:42:33 +0300
From:   Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
To:     linux-snps-arc@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Subject: [PATCH] ARC: HSDK: DTS: Temporary fix of sdio ciu frequency

DW sdio controller has external ciu clock devider 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 ciu clock and works unstable (see STAR 9001204800)

So add temporary fix and change clock frequency from 100000000
to 12500000 Hz until we fix dw sdio driver itself.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
---
 arch/arc/boot/dts/hsdk.dts | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arc/boot/dts/hsdk.dts b/arch/arc/boot/dts/hsdk.dts
index 8412669..b922f3f 100644
--- a/arch/arc/boot/dts/hsdk.dts
+++ b/arch/arc/boot/dts/hsdk.dts
@@ -127,7 +127,17 @@
 
 		mmcclk_ciu: mmcclk-ciu {
 			compatible = "fixed-clock";
-			clock-frequency = <100000000>;
+			/*
+			 * 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
+			 * works unstable (see STAR 9001204800)
+			 * So add temporary fix and change clock frequency
+			 * from 100000000 to 12500000 Hz until we fix dw sdio
+			 * driver itself.
+			 */
+			clock-frequency = <12500000>;
 			#clock-cells = <0>;
 		};
 
-- 
2.9.3