serial_core: add pci uart early console support

PATCH Superseded Bin Gao 2 participants 7 messages May 18, 2015 – May 20, 2015

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x86 TTY layer and serial drivers

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Bin Gao

author

2015-05-18 21:10 UTC #0 lore raw

PATCH v3 1/2 serial_core: add pci uart early console support

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 <[email protected]>

---
 arch/x86/Kconfig                 |  11 +++
 drivers/tty/serial/earlycon.c    |   9 +++
 drivers/tty/serial/serial_core.c | 145 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 163 insertions(+), 2 deletions(-)

arch/x86/Kconfig +11 -0

index 226d569..1283220 100644
@@ -2228,6 +2228,8 @@ config PCI
 	  your box. Other bus systems are ISA, EISA, MicroChannel (MCA) or
 	  VESA. If you have PCI, say Y, otherwise N.
 
+	select HAVE_EARLY_PCI
+
 choice
 	prompt "PCI access mode"
 	depends on X86_32 && PCI

@@ -2265,6 +2267,15 @@ config PCI_GOANY
 
 endchoice
 
+config HAVE_EARLY_PCI
+	def_bool y
+	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 must enable this option which is required  by arch
+	  independent codes, e.g. uart8250 pci early console driver.
+
 config PCI_BIOS
 	def_bool y
 	depends on X86_32 && PCI && (PCI_GOBIOS || PCI_GOANY)

drivers/tty/serial/earlycon.c +9 -0

index 6dc471e..63ae60e 100644
@@ -193,6 +193,15 @@ static int __init param_setup_earlycon(char *buf)
 }
 early_param("earlycon", param_setup_earlycon);
 
+/* x86 uses "earlyprintk=xxx", so we keep the compatibility here */
+#ifdef CONFIG_X86
+static int __init param_setup_earlycon_x86(char *buf)
+{
+	return param_setup_earlycon(buf);
+}
+early_param("earlyprintk", param_setup_earlycon_x86);
+#endif
+
 int __init of_setup_earlycon(unsigned long addr,
 			     int (*setup)(struct earlycon_device *, const char *))
 {

drivers/tty/serial/serial_core.c +143 -2

186 lines not on this page · raw message

Signature · 1 line

1.9.1

Paul Bolle

2015-05-19 12:01 UTC #1 lore raw

arch/x86/Kconfig config PCI · line 2232

Quoted 8 lines · Bin Gao

arch/x86/Kconfig +2 -0

@@ -2228,6 +2228,8 @@ config PCI
 	  your box. Other bus systems are ISA, EISA, MicroChannel (MCA) or
 	  VESA. If you have PCI, say Y, otherwise N.
 
+	select HAVE_EARLY_PCI
+

It's legal to have options after the help text of a Kconfig entry. It's also very uncommon to do that. Please put this select statement before the line reading "---help---" of the PCI entry.

arch/x86/Kconfig config PCI_GOANY · line 2271

Quoted 2 lines

arch/x86/Kconfig +2 -0
+config HAVE_EARLY_PCI
+	def_bool y

You probably want just
bool

here. Because this symbol has no further dependencies, which means HAVE_EARLY_PCI will now always be set to 'y'. That, in turn, makes the select you added above pointless.

arch/x86/Kconfig config PCI_GOANY · line 2275

Quoted 4 lines

arch/x86/Kconfig +4 -0

+	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

Is this expected to be used outside of X86?

arch/x86/Kconfig config PCI_GOANY · line 2278

Quoted 3 lines

arch/x86/Kconfig +3 -0

+	  early pci APIs must enable this option which is required  by arch
+	  independent codes, e.g. uart8250 pci early console driver.
+

Thanks,

Paul Bolle

Bin Gao

author

2015-05-19 17:20 UTC #2 lore raw

Quoted 7 lines · Paul Bolle

Quoted 6 lines · Bin Gao

arch/x86/Kconfig +0 -0

@@ -2228,6 +2228,8 @@ config PCI
 	  your box. Other bus systems are ISA, EISA, MicroChannel (MCA) or
 	  VESA. If you have PCI, say Y, otherwise N.

Quoted 7 lines

arch/x86/Kconfig config PCI · line 2232
Quoted 2 lines
arch/x86/Kconfig +2 -0
+	select HAVE_EARLY_PCI
+
It's legal to have options after the help text of a Kconfig entry. It's also very uncommon to do that. Please put this select statement before the line reading "---help---" of the PCI entry.

Will fix this in next patch set.

Quoted 10 lines

arch/x86/Kconfig config PCI_GOANY · line 2271
Quoted 2 lines
arch/x86/Kconfig +2 -0
+config HAVE_EARLY_PCI
+	def_bool y
You probably want just
bool
here. Because this symbol has no further dependencies, which means HAVE_EARLY_PCI will now always be set to 'y'. That, in turn, makes the select you added above pointless.

Yes, you're right. bool is better.

Quoted 6 lines

arch/x86/Kconfig config PCI_GOANY · line 2275
Quoted 4 lines
arch/x86/Kconfig +4 -0
+	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
Is this expected to be used outside of X86?

Yes, drivers/tty/serial/serial_core.c is going to use it.

Paul Bolle

2015-05-20 09:16 UTC #3 lore raw

Quoted 3 lines · Bin Gao

Quoted 1 line · Paul Bolle
Is this expected to be used outside of X86?
Yes, drivers/tty/serial/serial_core.c is going to use it.

What I should have asked is: do you expect architectures other than X86 to set HAVE_EARLY_PCI? Because then you should put that Kconfig entry in a file reachable by all architectures. Say, in init/Kconfig or in drivers/tty/serial/Kconfig.

(You can also have an entry for HAVE_EARLY_PCI for each arch that needs it, but that would be a bit silly.)

Thanks,

Paul Bolle

Bin Gao

author

2015-05-20 17:47 UTC #4 lore raw

Quoted 8 lines · Paul Bolle

What I should have asked is: do you expect architectures other than X86 to set HAVE_EARLY_PCI? Because then you should put that Kconfig entry in a file reachable by all architectures. Say, in init/Kconfig or in drivers/tty/serial/Kconfig.
(You can also have an entry for HAVE_EARLY_PCI for each arch that needs it, but that would be a bit silly.)

The HAVE_EARLY_PCI entry should be actually in generic PCI layer, i.e. drivers/pci, because it's a PCI feature but only some archs (currently only x86) support it.
Then an arch with this feature could announce it in arch/<arch>/Kconfig by:
select HAVE_EARLY_PCI if PCI

Paul Bolle

2015-05-20 17:50 UTC #5 lore raw

Quoted 5 lines · Bin Gao

The HAVE_EARLY_PCI entry should be actually in generic PCI layer, i.e. drivers/pci, because it's a PCI feature but only some archs (currently only x86) support it.
Then an arch with this feature could announce it in arch/<arch>/Kconfig by:
select HAVE_EARLY_PCI if PCI

That makes more sense. So v4 will put HAVE_EARLY_PCI in a Kconfig under drivers/pci/?

Thanks,

Paul Bolle

Bin Gao

author

2015-05-20 21:04 UTC #6 lore raw

Quoted 3 lines · Paul Bolle

That makes more sense. So v4 will put HAVE_EARLY_PCI in a Kconfig under drivers/pci/?

Yes.