[PATCH] powerpc: Add support for early debugging via Serial 16550 console

[Christophe Leroy]

Le 19/08/2022 à 23:12, Pali Rohár a écrit :
> 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/

Build failure if I select it on mpc885_ads_defconfig :

   LD      vmlinux.o
   MODPOST vmlinux.symvers
   MODINFO modules.builtin.modinfo
   GEN     modules.builtin
   CC      .vmlinux.export.o
   LD      .tmp_vmlinux.kallsyms1
powerpc64-linux-ld: arch/powerpc/kernel/udbg.o: in function 
`udbg_early_init':
/home/chleroy/linux-powerpc/arch/powerpc/kernel/udbg.c:71: undefined 
reference to `udbg_init_debug_16550'



> ---
>   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
> +

Putting it before EARLY_DEBUG_MEMCONS means that configs that were 
previously selectiong EARLY_DEBUG_MEMCONS will now select 
EARLY_DEBUG_16550 instead.

Add a dependency to PPC_UDBG_16550 to avoid the build failure I mentionned ?

>   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

A default value is necessary here to avoid prompts during defconfig builds.

> +
> +config PPC_EARLY_DEBUG_16550_STRIDE
> +	int "Early debug Serial 16550 stride"
> +	depends on PPC_EARLY_DEBUG_16550
> +	default 1
> +
>   config FAIL_IOMMU
>   	bool "Fault-injection capability for IOMMU"
>   	depends on FAULT_INJECTION
> diff --git a/arch/powerpc/include/asm/udbg.h b/arch/powerpc/include/asm/udbg.h
> index b4aa0d88ce2c..20b5a37ab772 100644
> --- a/arch/powerpc/include/asm/udbg.h
> +++ b/arch/powerpc/include/asm/udbg.h
> @@ -53,6 +53,7 @@ extern void __init udbg_init_ehv_bc(void);
>   extern void __init udbg_init_ps3gelic(void);
>   extern void __init udbg_init_debug_opal_raw(void);
>   extern void __init udbg_init_debug_opal_hvsi(void);
> +extern void __init udbg_init_debug_16550(void);

'extern' keywork is pointless and deprecated for function prototypes, 
please don't add new ones.

Checkpatch reports:

CHECK: extern prototypes should be avoided in .h files
#77: FILE: arch/powerpc/include/asm/udbg.h:56:
+extern void __init udbg_init_debug_16550(void);


>   
>   #endif /* __KERNEL__ */
>   #endif /* _ASM_POWERPC_UDBG_H */
> diff --git a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
> index b1544b2f6321..92b3fc258d11 100644
> --- a/arch/powerpc/kernel/udbg.c
> +++ b/arch/powerpc/kernel/udbg.c
> @@ -67,6 +67,8 @@ void __init udbg_early_init(void)
>   	udbg_init_debug_opal_raw();
>   #elif defined(CONFIG_PPC_EARLY_DEBUG_OPAL_HVSI)
>   	udbg_init_debug_opal_hvsi();
> +#elif defined(CONFIG_PPC_EARLY_DEBUG_16550)
> +	udbg_init_debug_16550();
>   #endif
>   
>   #ifdef CONFIG_PPC_EARLY_DEBUG
> diff --git a/arch/powerpc/kernel/udbg_16550.c b/arch/powerpc/kernel/udbg_16550.c
> index d3942de254c6..46f2d831d7c9 100644
> --- a/arch/powerpc/kernel/udbg_16550.c
> +++ b/arch/powerpc/kernel/udbg_16550.c
> @@ -8,6 +8,7 @@
>   #include <asm/udbg.h>
>   #include <asm/io.h>
>   #include <asm/reg_a2.h>
> +#include <asm/early_ioremap.h>
>   
>   extern u8 real_readb(volatile u8 __iomem  *addr);
>   extern void real_writeb(u8 data, volatile u8 __iomem *addr);
> @@ -335,3 +336,35 @@ void __init udbg_init_debug_microwatt(void)
>   }
>   
>   #endif /* CONFIG_PPC_EARLY_DEBUG_MICROWATT */
> +
> +#ifdef CONFIG_PPC_EARLY_DEBUG_16550
> +
> +static void __iomem *udbg_uart_early_addr;
> +
> +void __init udbg_init_debug_16550(void)
> +{
> +	udbg_uart_early_addr = early_ioremap(CONFIG_PPC_EARLY_DEBUG_16550_PHYSADDR, 0x1000);
> +	udbg_uart_init_mmio(udbg_uart_early_addr, CONFIG_PPC_EARLY_DEBUG_16550_STRIDE);
> +}
> +
> +static int __init udbg_init_debug_16550_ioremap(void)
> +{
> +	void __iomem *addr;
> +
> +	if (!udbg_uart_early_addr)
> +		return 0;
> +
> +	addr = ioremap(CONFIG_PPC_EARLY_DEBUG_16550_PHYSADDR, 0x1000);
> +	if (WARN_ON(!addr))
> +		return -ENOMEM;
> +
> +	udbg_uart_init_mmio(addr, CONFIG_PPC_EARLY_DEBUG_16550_STRIDE);
> +	early_iounmap(udbg_uart_early_addr, 0x1000);
> +	udbg_uart_early_addr = NULL;
> +
> +	return 0;
> +}
> +
> +early_initcall(udbg_init_debug_16550_ioremap);
> +
> +#endif /* CONFIG_PPC_EARLY_DEBUG_16550 */