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Date:	Sun, 28 Dec 2014 19:33:07 +0100
From:	Pavel Machek <pavel@....cz>
To:	Joe Perches <joe@...ches.com>
Cc:	linux-arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-m68k <linux-m68k@...ts.linux-m68k.org>,
	Steven Miao <realmz6@...il.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	linux-mips <linux-mips@...ux-mips.org>
Subject: Re: rfc: remove early_printk from a few arches? (blackfin, m68k,
 mips)

On Wed 2014-12-17 12:58:47, Joe Perches wrote:
> It seems like early_printk can be configured into
> a few architectures but also appear not to be used.
> 
> $ git grep -w "early_printk"
> arch/arm/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> arch/arm/kernel/early_printk.c: *  linux/arch/arm/kernel/early_printk.c
> arch/arm/mach-socfpga/socfpga.c:	early_printk("Early printk initialized\n");
> arch/blackfin/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK)           += early_printk.o
> arch/blackfin/kernel/bfin_dma.c:#include <asm/early_printk.h>
> arch/blackfin/kernel/early_printk.c: * derived from arch/x86/kernel/early_printk.c
> arch/blackfin/kernel/early_printk.c:#include <asm/early_printk.h>
> arch/blackfin/kernel/setup.c:#include <asm/early_printk.h>
> arch/blackfin/kernel/shadow_console.c:#include <asm/early_printk.h>
> arch/blackfin/mm/init.c:#include <asm/early_printk.h>
> arch/ia64/sn/kernel/setup.c:	 * IO on SN2 is done via SAL calls, early_printk won't work without this.
> arch/m68k/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> arch/microblaze/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> arch/microblaze/kernel/cpu/cpuinfo-pvr-full.c:	early_printk("ERROR: Microblaze " x "-different for PVR and DTS\n");
> arch/microblaze/kernel/cpu/cpuinfo-static.c:	early_printk("ERROR: Microblaze " x "-different for kernel and DTS\n");
> arch/microblaze/kernel/setup.c:/* initialize device tree for usage in early_printk */
> arch/mips/ath25/Makefile:obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
> arch/mips/ath79/Makefile:obj-$(CONFIG_EARLY_PRINTK)		+= early_printk.o
> arch/mips/bcm63xx/Makefile:obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> arch/mips/include/asm/mach-lantiq/falcon/lantiq_soc.h: * during early_printk no ioremap possible at this early stage
> arch/mips/include/asm/mach-lantiq/xway/lantiq_soc.h: * during early_printk no ioremap is possible
> arch/mips/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> arch/mips/lantiq/Makefile:obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
> arch/mips/loongson/common/Makefile:obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
> arch/mips/ralink/Makefile:obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
> arch/tile/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> arch/tile/kernel/early_printk.c:	early_printk("Kernel panic - not syncing: %pV", &vaf);
> arch/um/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
> arch/unicore32/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> arch/unicore32/kernel/early_printk.c: * linux/arch/unicore32/kernel/early_printk.c
> arch/x86/kernel/Makefile:obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> arch/x86/kernel/e820.c:	early_printk(msg);
> arch/x86/kernel/head64.c:		early_printk("Kernel alive\n");
> arch/x86/kernel/head_64.S:	call early_printk
> arch/x86/platform/efi/Makefile:obj-$(CONFIG_EARLY_PRINTK_EFI)	+= early_printk.o
> drivers/tty/serial/8250/8250_early.c: * and on early_printk.c by Andi Kleen.
> drivers/tty/serial/sn_console.c: * synchronous (raw) and asynchronous (buffered).  initially, early_printk
> drivers/tty/serial/sn_console.c:	/* without early_printk, we may be invoked late enough to race
> drivers/tty/serial/sn_console.c:	/* early_printk invocation may have done this for us */
> include/linux/printk.h:void early_printk(const char *fmt, ...);
> include/linux/printk.h:void early_printk(const char *s, ...) { }
> kernel/events/core.c:		early_printk("perf interrupt took too long (%lld > %lld), lowering "
> kernel/locking/lockdep.c: * We cannot printk in early bootup code. Not even early_printk()
> kernel/printk/printk.c:asmlinkage __visible void early_printk(const char *fmt, ...)
> kernel/printk/printk.c: * early_printk) - sometimes before setup_arch() completes - be careful
> kernel/printk/printk.c: * There are two types of consoles - bootconsoles (early_printk) and
> 
> These seem to the only uses:
> 
> arch/arm/mach-socfpga/socfpga.c:	early_printk("Early printk initialized\n");
> []
> arch/microblaze/kernel/cpu/cpuinfo-pvr-full.c:	early_printk("ERROR: Microblaze " x "-different for PVR and DTS\n");
> arch/microblaze/kernel/cpu/cpuinfo-static.c:	early_printk("ERROR: Microblaze " x "-different for kernel and DTS\n");
> []
> arch/tile/kernel/early_printk.c:	early_printk("Kernel panic - not syncing: %pV", &vaf);
> []
> arch/x86/kernel/e820.c:	early_printk(msg);
> arch/x86/kernel/head64.c:		early_printk("Kernel alive\n");
> arch/x86/kernel/head_64.S:	call early_printk
> []
> kernel/events/core.c:		early_printk("perf interrupt took too long (%lld > %lld), lowering "
> 
> So blackfin, m68k, and mips seems to have it possible to enable,
> but also don't appear at first glance to use it,
> 
> Is early_printk really used by these architectures?
> Should it be removed?

early_printk() is for debugging. Actually, feel free to remove:

arch/arm/mach-socfpga/socfpga.c:      early_printk("Early printk initialized\n");

Its debugging output I added and should have been removed. So... early_printk()s
_should_ be unused in the mainline code, but functionality should be
kept, so that when someone needs it, he can enable it.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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