[RFC PATCH] debugfs: add tools to printk 32-bit registers

[Alessandro Rubini <rubini@gnudd.com>]

Some debugfs file I deal with are mostly blocks of registers,
i.e. lines of the form "<name> = 0x<value>". Some files are only
registers, some include registers blocks among other material.  This
patch introduces data structures and functions to deal with both
cases.  I expect more users of this over time.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Giancarlo Asnaghi <giancarlo.asnaghi@st.com>
---

I'm using this code internally to clean up some heavy bricks of code I
received. For submission, I tried to use the new functions in the file
drivers/video/mbx/mbxdebugfs.c , but I found it is not compiling for a
number of not-really-trivial reasons, so I left it alone -- maybe it
should be removed altogether (it's associated driver compiles fine,
it's only the register dumps that don't).

 fs/debugfs/file.c       |   90 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/debugfs.h |   26 +++++++++++++
 2 files changed, 116 insertions(+), 0 deletions(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 90f7657..f31a27c 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -15,6 +15,7 @@
 
 #include <linux/module.h>
 #include <linux/fs.h>
+#include <linux/seq_file.h>
 #include <linux/pagemap.h>
 #include <linux/namei.h>
 #include <linux/debugfs.h>
@@ -525,3 +526,92 @@ struct dentry *debugfs_create_blob(const char *name, mode_t mode,
 	return debugfs_create_file(name, mode, parent, blob, &fops_blob);
 }
 EXPORT_SYMBOL_GPL(debugfs_create_blob);
+
+/*
+ * The regset32 stuff is used to print 32-bit registers using the
+ * seq_file utilities. We offer printing a register set in an already-opened
+ * sequential file or create a debugfs file that only prints a regset32.
+ */
+
+/**
+ * debugfs_print_regs32 - use seq_print to describe a set of registers
+ * @s: the seq_file structure being used to generate output
+ * @regs: an array if struct debugfs_reg32 structures
+ * @mregs: the length of the above array
+ * @base: the base address to be used in reading the registers
+ * @prefix: a string to be prefixed to every output line
+ *
+ * This function outputs a text block describing the current values of
+ * some 32-bit hardware registers. It is meant to be used within debugfs
+ * files based on seq_file that need to show registers, intermixed with other
+ * information. The prefix argument may be used to specify a leading string,
+ * because some peripherals have several blocks of identical registers,
+ * for example configuration of dma channels
+ */
+int debugfs_print_regs32(struct seq_file *s, struct debugfs_reg32 *regs,
+			   int nregs, void __iomem *base, char *prefix)
+{
+	int i, ret = 0;
+
+	for (i = 0; i < nregs; i++, regs++) {
+		if (prefix)
+			ret += seq_printf(s, "%s", prefix);
+		ret += seq_printf(s, "%s = 0x%08x\n", regs->name,
+				  readl((void *)(base + regs->offset)));
+	}
+	return ret;
+}
+EXPORT_SYMBOL_GPL(debugfs_print_regs32);
+
+static int debugfs_show_regset32(struct seq_file *s, void *data)
+{
+	struct debugfs_regset32 *regset = s->private;
+
+	debugfs_print_regs32(s, regset->regs, regset->nregs, regset->base, "");
+	return 0;
+}
+
+static int debugfs_open_regset32(struct inode *inode, struct file *file)
+{
+	return single_open(file, debugfs_show_regset32, inode->i_private);
+}
+
+static const struct file_operations fops_regset32 = {
+	.open =		debugfs_open_regset32,
+	.read =		seq_read,
+	.llseek =	seq_lseek,
+	.release =	single_release,
+};
+
+/**
+ * debugfs_create_regset32 - create a debugfs file that returns register values
+ * @name: a pointer to a string containing the name of the file to create.
+ * @mode: the permission that the file should have
+ * @parent: a pointer to the parent dentry for this file.  This should be a
+ *          directory dentry if set.  If this parameter is %NULL, then the
+ *          file will be created in the root of the debugfs filesystem.
+ * @regset: a pointer to a struct debugfs_regset32, which contains a pointer
+ *          to an array of register definitions, the array size and the base
+ *          address where the register bank is to be found.
+ *
+ * This function creates a file in debugfs with the given name that reports
+ * the names and values of a set of 32-bit registers. If the @mode variable
+ * is so set it can be read from. Writing is not supported.
+ *
+ * This function will return a pointer to a dentry if it succeeds.  This
+ * pointer must be passed to the debugfs_remove() function when the file is
+ * to be removed (no automatic cleanup happens if your module is unloaded,
+ * you are responsible here.)  If an error occurs, %NULL will be returned.
+ *
+ * If debugfs is not enabled in the kernel, the value -%ENODEV will be
+ * returned.  It is not wise to check for this value, but rather, check for
+ * %NULL or !%NULL instead as to eliminate the need for #ifdef in the calling
+ * code.
+ */
+struct dentry *debugfs_create_regset32(const char *name, mode_t mode,
+				       struct dentry *parent,
+				       struct debugfs_regset32 *regset)
+{
+	return debugfs_create_file(name, mode, parent, regset, &fops_regset32);
+}
+EXPORT_SYMBOL_GPL(debugfs_create_regset32);
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index e7d9b20..5e6b01f 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -16,6 +16,7 @@
 #define _DEBUGFS_H_
 
 #include <linux/fs.h>
+#include <linux/seq_file.h>
 
 #include <linux/types.h>
 
@@ -26,6 +27,17 @@ struct debugfs_blob_wrapper {
 	unsigned long size;
 };
 
+struct debugfs_reg32 {
+	char *name;
+	unsigned long offset;
+};
+
+struct debugfs_regset32 {
+	struct debugfs_reg32 *regs;
+	int nregs;
+	void __iomem *base;
+};
+
 extern struct dentry *arch_debugfs_dir;
 
 #if defined(CONFIG_DEBUG_FS)
@@ -74,6 +86,13 @@ struct dentry *debugfs_create_blob(const char *name, mode_t mode,
 				  struct dentry *parent,
 				  struct debugfs_blob_wrapper *blob);
 
+struct dentry *debugfs_create_regset32(const char *name, mode_t mode,
+				     struct dentry *parent,
+				     struct debugfs_regset32 *regset);
+
+int debugfs_print_regs32(struct seq_file *s, struct debugfs_reg32 *regs,
+			 int nregs, void __iomem *base, char *prefix);
+
 bool debugfs_initialized(void);
 
 #else
@@ -188,6 +207,13 @@ static inline struct dentry *debugfs_create_blob(const char *name, mode_t mode,
 	return ERR_PTR(-ENODEV);
 }
 
+static inline struct dentry *debugfs_create_regset32(const char *name,
+				   mode_t mode, struct dentry *parent,
+				   struct debugfs_regset32 *regset)
+{
+	return ERR_PTR(-ENODEV);
+}
+
 static inline bool debugfs_initialized(void)
 {
 	return false;
-- 
1.5.6.5