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

[Gabriel Paubert <paubert@iram.es>]

On Mon, Aug 22, 2022 at 05:33:35PM +0200, Pali Rohár wrote:
> On Monday 22 August 2022 14:25:57 Christophe Leroy wrote:
> > 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@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 ?
> 
> Yea, there is really missing dependency. I will fix it.
> 
> > >   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.
> 
> I used extern keyword to follow existing coding style.

In this case it's better to remove existing extern specifications in the
surrounding lines. Increasing a bit the footprint of the patch is
justified, and does not significantly increase the risk of conflicts
with other patches, unlike the gratuitous churn we see sometimes.

	Gabriel
> 
> > 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 */