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Date:   Sat, 24 Sep 2022 14:10:52 +0200
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Nick Child <nick.child@ibm.com>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] powerpc: Add support for early debugging via Serial
 16550 console
Message-ID: <20220924121052.xh56s4orfty4nj5x@pali>
References: <20220819211254.22192-1-pali@kernel.org>
 <20220822231501.16827-1-pali@kernel.org>
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Hello! Is something else needed for this v2 patch?

On Tuesday 23 August 2022 01:15:01 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@kernel.org>
> ---
> Changes in v2:
> * Move PPC_EARLY_DEBUG_16550 after PPC_EARLY_DEBUG_MEMCONS, so memcons stay default
> * Add missing dependency on PPC_UDBG_16550
> ---
> 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       | 15 +++++++++++++++
>  arch/powerpc/include/asm/udbg.h  |  1 +
>  arch/powerpc/kernel/udbg.c       |  2 ++
>  arch/powerpc/kernel/udbg_16550.c | 33 ++++++++++++++++++++++++++++++++
>  4 files changed, 51 insertions(+)
> 
> diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
> index 9f363c143d86..ad7238d28fa9 100644
> --- a/arch/powerpc/Kconfig.debug
> +++ b/arch/powerpc/Kconfig.debug
> @@ -283,6 +283,12 @@ config PPC_EARLY_DEBUG_MEMCONS
>  	  This console provides input and output buffers stored within the
>  	  kernel BSS and should be safe to select on any system. A debugger
>  	  can then be used to read kernel output or send input to the console.
> +
> +config PPC_EARLY_DEBUG_16550
> +	bool "Serial 16550"
> +	depends on PPC_UDBG_16550
> +	help
> +	  Select this to enable early debugging via Serial 16550 console
>  endchoice
>  
>  config PPC_MEMCONS_OUTPUT_SIZE
> @@ -355,6 +361,15 @@ 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
> +
> +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);
>  
>  #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 */
> -- 
> 2.20.1
>