[PATCH linux v3] arm: aspeed: zaius: Disable LPC reset for UART1

[Xo Wang]

Currently, UART1 on Zaius BMC is unusable until brought out of reset by
powering the host on. In that default reset state, ttyS0 can still be
opened and UART1 silently drops bytes, which is not obviously expected
behavior.

Clear the LPC block control bit that enables LPCRST# as a reset source
for UART1, making UART1 immediately useful in that it won't discard
bytes.

Signed-off-by: Xo Wang <xow at google.com>
---
 arch/arm/mach-aspeed/aspeed.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm/mach-aspeed/aspeed.c b/arch/arm/mach-aspeed/aspeed.c
index 4bd3680d742d..b7022eaa7b5d 100644
--- a/arch/arm/mach-aspeed/aspeed.c
+++ b/arch/arm/mach-aspeed/aspeed.c
@@ -185,6 +185,14 @@ static void __init do_zaius_setup(void)
 
 	/* Set SPI1 CE0 decoding window to 0x30000000 */
 	writel(0x68600000, AST_IO(AST_BASE_SPI | 0x30));
+
+	/* Disable default behavior of UART1 being held in reset by LPCRST#.
+	 * By releasing UART1 from being controlled by LPC reset, it becomes
+	 * immediately available regardless of the host being up.
+	 * */
+	reg = readl(AST_IO(AST_BASE_LPC | 0x98));
+	/* Clear "Enable UART1 reset source from LPC" */
+	writel(reg & ~BIT(4), AST_IO(AST_BASE_LPC | 0x98));
 }
 
 static void __init do_witherspoon_setup(void)
-- 
2.11.0.483.g087da7b7c-goog