[PATCH v5 1/2] serial_core: add pci uart early console support

From: Bin Gao
Date: Fri May 29 2015 - 14:27:08 EST

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@xxxxxxxxx>
---
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
+ 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
+
/*
* This is used to lock changes in serial line configuration.
*/
@@ -1808,6 +1813,85 @@ uart_get_console(struct uart_port *ports, int nr, struct console *co)
return ports + idx;
}

+#ifdef CONFIG_PCI_EARLY
+/*
+ * The whole pci option from the command line is: pci[32],B:D.F[,options]
+ * Examples:
+ * pci,0:21.3,115200n8
+ * pci32,0:21.3
+ * Here pci32 means 8250 UART registers are 32-bit width(regshift = 2).
+ * pci means 8250 UART registers are 8-bit width(regshift = 0).
+ * B,D and F are bus, device and function, in decimal(not hex).
+ * The additional options(115200n8) would be parsed by the earlycon framework.
+ *
+ * @options: the pci options
+ * @phys: the pointer to return pci mem or io address
+ * return: <0: error
+ * 0: pci mem
+ * 1: pci io
+ */
+static int parse_pci_options(char *options, unsigned long *phys)
+{
+ u8 bus, dev, func;
+ u64 bar0;
+ u16 cmd;
+ int pci_io = 0;
+
+ if (!early_pci_allowed()) {
+ pr_err("earlycon: early pci not allowed.\n");
+ return -EINVAL;
+ }
+
+ /* We come here with options=B:D.F[,options] */
+ if (*options == 0)
+ goto failed;
+
+ bus = (u8)simple_strtoul(options, &options, 10);
+ if (*options != ':')
+ goto failed;
+
+ dev = (u8)simple_strtoul(options + 1, &options, 10);
+ if (*options != '.')
+ goto failed;
+
+ func = (u8)simple_strtoul(options + 1, NULL, 10);
+
+ bar0 = read_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0);
+
+ /* The BAR is IO or Memory? */
+ if ((bar0 & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO)
+ pci_io = 1;
+
+ if ((bar0 & PCI_BASE_ADDRESS_MEM_TYPE_MASK) ==
+ PCI_BASE_ADDRESS_MEM_TYPE_64)
+ bar0 |= (u64)read_pci_config(bus, dev, func,
+ PCI_BASE_ADDRESS_0 + 4) << 32;
+
+ *phys = bar0 & (pci_io ? PCI_BASE_ADDRESS_IO_MASK :
+ PCI_BASE_ADDRESS_MEM_MASK);
+
+ /* Enable address decoding */
+ cmd = read_pci_config_16(bus, dev, func, PCI_COMMAND);
+ write_pci_config_16(bus, dev, func, PCI_COMMAND,
+ cmd | (pci_io ? PCI_COMMAND_IO : PCI_COMMAND_MEMORY));
+
+ pr_debug("Use 8250 uart at PCI 0000:%02u:%02u.%01u as early console\n",
+ bus, dev, func);
+ return pci_io;
+
+failed:
+ pr_err("Invalid earlycon pci parameters\n");
+ return -EINVAL;
+}
+
+#else
+static int parse_pci_options(char *options, unsigned long *phys)
+{
+ pr_err("earlycon: pci not supported (requires CONFIG_PCI_EARLY=y)\n");
+ return -EINVAL;
+}
+#endif
+
/**
* uart_parse_earlycon - Parse earlycon options
* @p: ptr to 2nd field (ie., just beyond '<name>,')
@@ -1817,7 +1901,9 @@ uart_get_console(struct uart_port *ports, int nr, struct console *co)
*
* Decodes earlycon kernel command line parameters of the form
* earlycon=<name>,io|mmio|mmio32,<addr>,<options>
+ * earlycon=<name>,pci|pci32,<bus:dev.func>,<options>
* console=<name>,io|mmio|mmio32,<addr>,<options>
+ * For pci|pci32, bus, dev and func are in decimal.
*
* The optional form
* earlycon=<name>,0x<addr>,<options>
@@ -1829,22 +1915,40 @@ uart_get_console(struct uart_port *ports, int nr, struct console *co)
int uart_parse_earlycon(char *p, unsigned char *iotype, unsigned long *addr,
char **options)
{
+ int ret;
+ unsigned long phys;
+
if (strncmp(p, "mmio,", 5) == 0) {
*iotype = UPIO_MEM;
p += 5;
+ *addr = simple_strtoul(p, NULL, 0);
} else if (strncmp(p, "mmio32,", 7) == 0) {
*iotype = UPIO_MEM32;
p += 7;
+ *addr = simple_strtoul(p, NULL, 0);
+ } else if (strncmp(p, "pci,", 4) == 0) {
+ p += 4;
+ ret = parse_pci_options(p, &phys);
+ if (ret < 0)
+ return ret;
+ *iotype = (ret > 0) ? UPIO_PORT : UPIO_MEM;
+ } else if (strncmp(p, "pci32,", 6) == 0) {
+ p += 6;
+ ret = parse_pci_options(p, &phys);
+ if (ret < 0)
+ return ret;
+ *iotype = (ret > 0) ? UPIO_PORT : UPIO_MEM32;
} else if (strncmp(p, "io,", 3) == 0) {
*iotype = UPIO_PORT;
p += 3;
+ *addr = simple_strtoul(p, NULL, 0);
} else if (strncmp(p, "0x", 2) == 0) {
*iotype = UPIO_MEM;
+ *addr = simple_strtoul(p, NULL, 0);
} else {
return -EINVAL;
}

- *addr = simple_strtoul(p, NULL, 0);
p = strchr(p, ',');
if (p)
p++;
--
1.9.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/