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[v3,1/2] Documentation: arm: early_ioremap/early_memremap

Message ID 1380793756-2562-2-git-send-email-leif.lindholm@linaro.org (mailing list archive)
State New, archived
Headers show

Commit Message

Leif Lindholm Oct. 3, 2013, 9:49 a.m. UTC 
This patch provides documentation of the early_ioremap() and
early_memremap() functionality,including its implementation and usage
instructions.

Cc: linux-doc@vger.kernel.org
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Arnd Bergman <arnd@arndb.de>  
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Rob Landley <rob@landley.net>

---
 Documentation/arm/00-INDEX          |    2 ++
 Documentation/arm/early_ioremap.txt |   23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 Documentation/arm/early_ioremap.txt
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Patch

diff --git a/Documentation/arm/00-INDEX b/Documentation/arm/00-INDEX
index 36420e1..4978456 100644
--- a/Documentation/arm/00-INDEX
+++ b/Documentation/arm/00-INDEX
@@ -24,6 +24,8 @@  SPEAr
 	- ST SPEAr platform Linux Overview
 VFP/
 	- Release notes for Linux Kernel Vector Floating Point support code
+early_ioremap.txt
+	- documentation of the early_ioremap() functionality
 empeg/
 	- Ltd's Empeg MP3 Car Audio Player
 mem_alignment
diff --git a/Documentation/arm/early_ioremap.txt b/Documentation/arm/early_ioremap.txt
new file mode 100644
index 0000000..6096cfa
--- /dev/null
+++ b/Documentation/arm/early_ioremap.txt
@@ -0,0 +1,23 @@ 
+early_ioremap()/early_memremap() and early_iounmap() provide a mechanism for
+temporarily mapping in small blocks of memory, identified by their physical
+address, into the fixmap virtual address block before paging_init() has run
+and more flexible mapping functions are available.
+
+Due to its direct method, it also gets around potential need for special
+handling of regions that end up in highmem.
+
+It supports up to 7 simultaneously mapped regions of up to 128KB each.
+All mappings created by early_ioremap() are non-shareable device memory.
+All mappings created by early_memremap() are uncached normal memory.
+
+Any residual mappings will be overridden by subsequent kmap() calls (but do
+use early_iounmap()).
+
+Specify 'early_ioremap_debug' on the kernel commandline for verbose output.
+
+SYNOPSIS
+	#include <linux/io.h>
+
+	void *early_ioremap(resource_size_t phys_addr, unsigned long size);
+	void *early_memremap(resource_size_t phys_addr, unsigned long size);
+	void early_iounmap(void *addr, unsigned long size);