[PATCH] powerpc: Add support for early debugging via Serial 16550 console
Randy Dunlap
rdunlap at infradead.org
Sat Aug 20 08:43:18 AEST 2022
On 8/19/22 15:38, Pali Rohár wrote:
> On Friday 19 August 2022 15:34:14 Randy Dunlap wrote:
>> Hi--
>>
>> On 8/19/22 14:12, Pali Rohár wrote:
>>> Currently powerpc early debugging contains lot of platform specific
>>> options, but does not support standard UART / serial 16550 console.
>>>
>>> Later legacy_serial.c code supports registering UART as early debug console
>>> from device tree but it is not early during booting, but rather later after
>>> machine description code finishes.
>>>
>>> So for real early debugging via UART is current code unsuitable.
>>>
>>> Add support for new early debugging option CONFIG_PPC_EARLY_DEBUG_16550
>>> which enable Serial 16550 console on address defined by new option
>>> CONFIG_PPC_EARLY_DEBUG_16550_PHYSADDR and by stride by option
>>> CONFIG_PPC_EARLY_DEBUG_16550_STRIDE.
>>>
>>> With this change it is possible to debug powerpc machine descriptor code.
>>> For example this early debugging code can print on serial console also
>>> "No suitable machine description found" error which is done before
>>> legacy_serial.c code.
>>>
>>> Signed-off-by: Pali Rohár <pali at kernel.org>
>>> ---
>>> Tested on P2020 board. It allowed me do debug and implement this patch series:
>>> https://lore.kernel.org/linuxppc-dev/20220819191557.28116-1-pali@kernel.org/
>>> ---
>>> arch/powerpc/Kconfig.debug | 14 ++++++++++++++
>>> arch/powerpc/include/asm/udbg.h | 1 +
>>> arch/powerpc/kernel/udbg.c | 2 ++
>>> arch/powerpc/kernel/udbg_16550.c | 33 ++++++++++++++++++++++++++++++++
>>> 4 files changed, 50 insertions(+)
>>>
>>> diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
>>> index 9f363c143d86..a4e7d90a45d2 100644
>>> --- a/arch/powerpc/Kconfig.debug
>>> +++ b/arch/powerpc/Kconfig.debug
>>> @@ -276,6 +276,11 @@ config PPC_EARLY_DEBUG_OPAL_HVSI
>>> Select this to enable early debugging for the PowerNV platform
>>> using an "hvsi" console
>>>
>>> +config PPC_EARLY_DEBUG_16550
>>> + bool "Serial 16550"
>>> + help
>>> + Select this to enable early debugging via Serial 16550 console
>>> +
>>> config PPC_EARLY_DEBUG_MEMCONS
>>> bool "In memory console"
>>> help
>>> @@ -355,6 +360,15 @@ config PPC_EARLY_DEBUG_CPM_ADDR
>>> platform probing is done, all platforms selected must
>>> share the same address.
>>>
>>> +config PPC_EARLY_DEBUG_16550_PHYSADDR
>>> + hex "Early debug Serial 16550 physical address"
>>> + depends on PPC_EARLY_DEBUG_16550
>>
>> Is there any chance that you could provide a default value here
>> so that 'make olddefconfig' does not end up like it does
>> without having a default value?
>
> No. Because there is not any default value. Physical address of 16550 is
> hardly HW dependent. Possibly also bootloader dependent (if it can remap
> peripherals to different physical addresses).
>
> User _has to_ specify correct physical address if want to use early
> debug 16550 console.
OK, we'll see if it ever causes a real problem then...
>> CONFIG_PPC_EARLY_DEBUG_16550=y
>> # CONFIG_PPC_EARLY_DEBUG_MEMCONS is not set
>> CONFIG_PPC_EARLY_DEBUG_16550_PHYSADDR=
>> CONFIG_PPC_EARLY_DEBUG_16550_STRIDE=1
>>
>> which then causes a kconfig prompt when starting
>> the build...
>
> Cannot we set somehow that PPC_EARLY_DEBUG_16550 would be disabled by
> default when upgrading defconfig?
Don't know about that.
Thanks.
--
~Randy
More information about the Linuxppc-dev
mailing list