[PATCH] arm: kirkwood: 88f6281: Detect CONFIG_SYS_TCLK from SAR register

[Pali Rohár]

Bit 21 in SAR register specifies if TCLK is running at 166 MHz or 200 MHz.
This information is undocumented in public Marvell Kirkwood Functional
Specifications [2], but is available in Linux v3.15 kirkwood code [1].

Commit 8ac303d49f89 ("arm: kirkwood: Do not overwrite CONFIG_SYS_TCLK")
broke support for Marvell 88F6281 SoCs because it was expected that all
those SoCs have TCLK running at 200 MHz as specified in Marvell 88F6281
Hardware Specifications [3].

Fix broken support for 88F6281 by detecting CONFIG_SYS_TCLK from SAR
register, like it was doing Linux v3.15.

[1] - https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/arm/mach-kirkwood/common.c?h=v3.15#n542
[2] - https://web.archive.org/web/20130730091033/http://www.marvell.com/embedded-processors/kirkwood/assets/FS_88F6180_9x_6281_OpenSource.pdf
[3] - https://web.archive.org/web/20120620073511/http://www.marvell.com/embedded-processors/kirkwood/assets/HW_88F6281_OpenSource.pdf

Fixes: 8ac303d49f89 ("arm: kirkwood: Do not overwrite CONFIG_SYS_TCLK")
Signed-off-by: Pali Rohár <pali at kernel.org>
---
Michael, please test this patch, if it fixes your boards.
---
 arch/arm/mach-kirkwood/include/mach/kw88f6281.h | 3 ++-
 arch/arm/mach-kirkwood/include/mach/soc.h       | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-kirkwood/include/mach/kw88f6281.h b/arch/arm/mach-kirkwood/include/mach/kw88f6281.h
index 87406081cf54..f86cd0bb6013 100644
--- a/arch/arm/mach-kirkwood/include/mach/kw88f6281.h
+++ b/arch/arm/mach-kirkwood/include/mach/kw88f6281.h
@@ -15,6 +15,7 @@
 #define KW_REGS_PHY_BASE		KW88F6281_REGS_PHYS_BASE
 
 /* TCLK Core Clock definition */
-#define CONFIG_SYS_TCLK	200000000 /* 200MHz */
+#define CONFIG_SYS_TCLK			((readl(CONFIG_SAR_REG) & BIT(21)) ? \
+					166666667 : 200000000)
 
 #endif /* _ASM_ARCH_KW88F6281_H */
diff --git a/arch/arm/mach-kirkwood/include/mach/soc.h b/arch/arm/mach-kirkwood/include/mach/soc.h
index 1d7f2828cd38..5f545c6f4349 100644
--- a/arch/arm/mach-kirkwood/include/mach/soc.h
+++ b/arch/arm/mach-kirkwood/include/mach/soc.h
@@ -62,6 +62,8 @@
 #define MVCPU_WIN_ENABLE	KWCPU_WIN_ENABLE
 #define MVCPU_WIN_DISABLE	KWCPU_WIN_DISABLE
 
+#define CONFIG_SAR_REG		(KW_MPP_BASE + 0x0030)
+
 #if defined (CONFIG_KW88F6281)
 #include <asm/arch/kw88f6281.h>
 #elif defined (CONFIG_KW88F6192)
-- 
2.20.1