Mason [off-list ref] writes:

On 27/10/2015 13:57, Mans Rullgard wrote:

quoted

Some SoCs have a Palmchip UART with a non-standard register layout.
This allows the debug console to work with these.

Signed-off-by: Mans Rullgard <redacted>
---
 arch/arm/Kconfig.debug        |  8 ++++++++
 arch/arm/include/debug/8250.S | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 0cfd7f9..9039fff 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug

@@ -1597,6 +1597,14 @@ config DEBUG_UART_8250_WORD
 		DEBUG_BCM_KONA_UART || DEBUG_RK32_UART2 || \
 		DEBUG_BRCMSTB_UART
 
+config DEBUG_UART_8250_PALMCHIP
+	bool "8250 UART is Palmchip variant"
+	depends on DEBUG_LL_UART_8250 || DEBUG_UART_8250

I am 100% clueless about the UART sequence in Linux.

There's earlyprintk, the boot console (polled?), the "full-blown"
console (with IRQs)...

If I want earlyprintk, I have to enable DEBUG_LL (?) so I'll have
DEBUG_LL_UART_8250, right? There's no way to pick DEBUG_UART_8250
in menuconfig, is there?

So I picked the following options:

CONFIG_DEBUG_LL=y
# CONFIG_DEBUG_ICEDCC is not set
# CONFIG_DEBUG_SEMIHOSTING is not set
CONFIG_DEBUG_LL_UART_8250=y
# CONFIG_DEBUG_LL_UART_PL01X is not set
CONFIG_DEBUG_LL_INCLUDE="debug/8250.S"
# CONFIG_DEBUG_UART_8250 is not set
# CONFIG_DEBUG_UART_BCM63XX is not set
CONFIG_DEBUG_UART_PHYS=0x10700
CONFIG_DEBUG_UART_VIRT=0xf0010700
CONFIG_DEBUG_UART_8250_SHIFT=2
CONFIG_DEBUG_UART_8250_WORD=y
CONFIG_DEBUG_UART_8250_PALMCHIP=y
# CONFIG_DEBUG_UART_8250_FLOW_CONTROL is not set
CONFIG_DEBUG_UNCOMPRESS=y
CONFIG_UNCOMPRESS_INCLUDE="debug/uncompress.h"
CONFIG_EARLY_PRINTK=y

Those are the settings I use.

I suppose I have to provide DEBUG_UART_PHYS because it needs
the address before it can parse the DT? But how am I supposed
to know the virtual address? Isn't that from iomap(UART_PHYS)?

The decompression code and early setup don't have that luxury.

'make' wouldn't let me proceed unless I gave something...

Then I have to add earlyprintk to my boot command line, right?
Do I need to specify more than that?

Just earlyprintk without any parameters works.

-- 
M?ns Rullg?rd
mans at mansr.com