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    Subject[PATCH] powerpc: Add support for early debugging via Serial 16550 console
    Date
    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/
    ---
    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
    +
    +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
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