[PATCH] KVM/arm: kernel low level debug support for ARM32 virtual platforms
Christopher Covington
cov at codeaurora.org
Tue Nov 3 08:33:17 PST 2015
Hi Mario,
On 11/02/2015 06:51 PM, Mario Smarduch wrote:
> Hello,
> this is a re-post from couple weeks ago, please take time to review this
> simple patch which simplifies DEBUG_LL and prevents kernel crash on virtual
> platforms.
>
> Before this patch DEBUG_LL for 'dummy virtual machine':
>
> ( ) Kernel low-level debugging via EmbeddedICE DCC channel
> ( ) Kernel low-level debug output via semihosting I/O
> ( ) Kernel low-level debugging via 8250 UART
> ( ) Kernel low-level debugging via ARM Ltd PL01x Primecell
>
> In summary if debug uart is not emulated kernel crashes.
> And once you pass that hurdle, uart physical/virtual addresses are unknown.
> DEBUG_LL comes in handy on many occasions and should be somewhat
> intuitive to use like it is for physical platforms. For virtual platforms
> user may start daubting the host and get into a bigger mess.
>
> After this patch is applied user gets:
>
> (X) Kernel low-level debugging on QEMU Virtual Platform
> ( ) Kernel low-level debugging on Kvmtool Virtual Platform
> ..... above repeated ....
>
> The virtual addresses selected follow arm reference models, high in vmalloc
> section with high mem enabled and guest running with >= 1GB of memory. The
> offset is leftover from arm reference models.
Which model? It doesn't appear to match the vexpress AEM/RTSM/FVP/whatever
which used 0x1c090000 for UART0.
> The patch is against 4.2.0-rc2 commit 43297dda0a51
>
> Original Description
> --------------------
> 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.
>
> Acked-by: Christoffer Dall <christoffer.dall at linaro.org>
> Signed-off-by: Mario Smarduch <m.smarduch at samsung.com>
> ---
> 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
I thought the only guarantee the virt machine had about the memory map was
that it would be described in the device tree.
> + 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
>
Regards,
Christopher Covington
--
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