[PATCH] KVM/arm: kernel low level debug suport for ARM32 virtual platforms

[Christoffer Dall]

On Fri, Oct 16, 2015 at 08:19:59PM -0700, Mario Smarduch wrote:
> When booting a VM using QEMU or Kvmtool there are no clear ways to 
> enable low level debugging for these virtual platforms. some menu port 
> choices are not supported by the virtual platforms at all. And there is no
> help on the location of physical and virtual addresses for the ports.
> This may lead to wrong debug port and a frozen VM with a blank screen.
> 
> This patch adds menu selections for QEMU and Kvmtool virtual platforms for low 
> level kernel print debugging. Help section displays port physical and
> virutal addresses.
> 
> ARM reference models use the MIDR register to run-time select UART port address 
> (for ARCH_VEXPRESS) based on A9 or A15 part numbers. Looked for a same approach
> but couldn't find a way to differentiate between virtual platforms, something
> like a platform register.
> 
> Signed-off-by: Mario Smarduch <m.smarduch at samsung.com>
> ---

I can't think of any better way to do this and I would be happy to see
this functionality in Linux, so:

Acked-by: Christoffer Dall <christoffer.dall at linaro.org>

>  arch/arm/Kconfig.debug | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> index a2e16f9..d126bd4 100644
> --- a/arch/arm/Kconfig.debug
> +++ b/arch/arm/Kconfig.debug
> @@ -1155,6 +1155,28 @@ choice
>  		  This option selects UART0 on VIA/Wondermedia System-on-a-chip
>  		  devices, including VT8500, WM8505, WM8650 and WM8850.
>  
> +	config DEBUG_VIRT_UART_QEMU
> +		bool "Kernel low-level debugging on QEMU Virtual Platform"
> +		depends on ARCH_VIRT
> +		select DEBUG_UART_PL01X
> +		help
> +		  Say Y here if you want the debug print routines to direct
> +		  their output to PL011 UART port on QEMU Virtual Platform.
> +		  Appropriate address values are:
> +			PHYS		VIRT
> +			0x9000000	0xf8090000
> +
> +	config DEBUG_VIRT_UART_KVMTOOL
> +		bool "Kernel low-level debugging on Kvmtool Virtual Platform"
> +		depends on ARCH_VIRT
> +		select DEBUG_UART_8250
> +		help
> +		  Say Y here if you want the debug print routines to direct
> +		  their output to 8250 UART port on Kvmtool Virtual
> +		  Platform. Appropriate address values are:
> +			PHYS		VIRT
> +			0x3f8		0xf80903f8
> +
>  	config DEBUG_ICEDCC
>  		bool "Kernel low-level debugging via EmbeddedICE DCC channel"
>  		help
> -- 
> 1.9.1
>