Re: [PATCH v6 1/2] serial_core: add pci uart early console support

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Jun 08, 2015 at 11:17:11AM -0700, Bin Gao wrote:
> On some Intel Atom SoCs, the legacy IO port UART(0x3F8) is not available.
> Instead, a 8250 compatible PCI uart can be used as early console.
> This patch adds pci support to the 8250 early console driver uart8250.
> For example, to enable pci uart(00:21.3) as early console on these
> platforms, append the following line to the kernel command line
> (assume baud rate is 115200):
> earlyprintk=uart8250,pci32,0:24.2,115200n8
> 
> Signed-off-by: Bin Gao <bin.gao@intel.com>
> ---
> Changes in v6: None
> Changes in v5:
>  - updated Documentation/kernel-parameters.txt.
>  - moved earlyprintk= to patch 2/2 (requires x86 people's review).
>  - rolled back to simple_strto* APIs.
>  - seperate pci/pci32 format description.
>  - minor error and debug message changes.
>  - if/else statements in uart_parse_earlycon() were refactored to avoid
>    logic steering locals.
> Changes in v4:
>  - moved PCI_EARLY definition from arch/x86/Kconfig to drivers/pci/Kconfig
>  - made earlycon= for all archs but earlyprintk= only for x86 by changing
>    "#ifdef #else #endif" to "#if #endif".
> Changes in v3:
>  - introduced CONFIG_EARLY_PCI to protect pci codes in serial_core.c.
>  - added earlyprintk= as alia to earlycon= to keep x86 compatibility.
> changes in v2:
>  - added the second patch (2/2) to remove existed pci early console support
>    from arch/x86/kernel/early_printk.c.
>  Documentation/kernel-parameters.txt |  15 +++++
>  arch/x86/Kconfig                    |   1 +
>  drivers/pci/Kconfig                 |  11 ++++
>  drivers/tty/serial/serial_core.c    | 106 +++++++++++++++++++++++++++++++++++-
>  4 files changed, 132 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 61ab162..598606e 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -969,6 +969,16 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			same format described for "console=ttyS<n>"; if
>  			unspecified, the h/w is not initialized.
>  
> +		uart8250,pci,<bus:dev.func>[,options]
> +		uart8250,pci32,<bus:dev.func>[,options]
> +			Start an early, polled-mode console on the 8250/16550
> +			UART at the specified PCI device (bus:dev.func).
> +			The io or memory mmaped register width is either 8-bit
> +			(pci) or 32-bit (pci32).
> +			'options' are specified in the same format described
> +			for "console=ttyS<n>"; if unspecified, the h/w is not
> +			initialized.
> +
>  		pl011,<addr>
>  			Start an early, polled-mode console on a pl011 serial
>  			port at the specified address. The pl011 serial port
> @@ -1009,6 +1019,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			earlyprintk=serial[,0x...[,baudrate]]
>  			earlyprintk=ttySn[,baudrate]
>  			earlyprintk=dbgp[debugController#]
> +			earlyprintk=uart8250,pci,<bus:dev.fun>[,options]
> +			earlyprintk=uart8250,pci32,<bus:dev.func>[,options]
>  
>  			earlyprintk is useful when the kernel crashes before
>  			the normal console is initialized. It is not enabled by
> @@ -1037,6 +1049,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  
>  			The xen output can only be used by Xen PV guests.
>  
> +			The uart8250,pci and uart8250,pci32 output share the
> +			same definition that is in earlycon= section.
> +
>  	edac_report=	[HW,EDAC] Control how to report EDAC event
>  			Format: {"on" | "off" | "force"}
>  			on: enable EDAC to report H/W event. May be overridden
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 226d569..bdedd61 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -143,6 +143,7 @@ config X86
>  	select ACPI_LEGACY_TABLES_LOOKUP if ACPI
>  	select X86_FEATURE_NAMES if PROC_FS
>  	select SRCU
> +	select PCI_EARLY if PCI
>  
>  config INSTRUCTION_DECODER
>  	def_bool y
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 7a8f1c5..4f0f055 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -114,4 +114,15 @@ config PCI_LABEL
>  	def_bool y if (DMI || ACPI)
>  	select NLS
>  
> +config PCI_EARLY
> +	bool "Early PCI access"
> +	depends on PCI
> +	default n

Default is always 'n' so this isn't needed here.


> +	help
> +	  This option indicates that a group of APIs are available (in
> +	  asm/pci-direct.h) so the kernel can access pci config registers
> +	  before the PCI subsystem is initialized. Any arch that supports
> +	  early pci APIs should enable this option which is required  by
> +	  arch independent codes, e.g. uart8250 pci early console driver.
> +
>  source "drivers/pci/host/Kconfig"
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 0b7bb12..5b21999 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -34,10 +34,15 @@
>  #include <linux/serial_core.h>
>  #include <linux/delay.h>
>  #include <linux/mutex.h>
> +#include <linux/pci_regs.h>
>  
>  #include <asm/irq.h>
>  #include <asm/uaccess.h>
>  
> +#ifdef CONFIG_PCI_EARLY
> +#include <asm/pci-direct.h>
> +#endif

You shouldn't need an #ifdef here, the .h file should handle it.  Why
doesn't pci.h always include this if it is present?

thanks,

greg k-h