generic: routerboot sysfs platform driver

This driver exposes the data encoded in the "hard_config" flash segment
of MikroTik RouterBOARDs devices. It presents the data in a sysfs folder
named "hard_config". The WLAN calibration data is available on demand via
the 'wlan_data' sysfs file in that folder.

This driver permanently allocates a chunk of RAM as large as the
"hard_config" MTD partition (typically 4KB), although it is technically
possible to operate entirely from the MTD device without using a local
buffer (except when requesting WLAN calibration data), at the cost of a
performance penalty.

This driver does not reuse any of the existing code previously found in
routerboot.c.

This driver has been successfully tested on BE (ath79) and LE (ipq40xx
and ramips) hardware.

Tested-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>
Tested-by: Baptiste Jonglez <git@bitsofnetworks.org>
Tested-by: Tobias Schramm <t.schramm@manjaro.org>
Tested-by: Christopher Hill <ch6574@gmail.com>
Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>

1 files changed, 183 insertions, 0 deletions

diff --git a/target/linux/generic/files/drivers/platform/mikrotik/routerboot.c b/target/linux/generic/files/drivers/platform/mikrotik/routerboot.c
new file mode 100644
index 0000000000..172db02533
--- /dev/null
+++ b/target/linux/generic/files/drivers/platform/mikrotik/routerboot.c
@@ -0,0 +1,183 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for MikroTik RouterBoot flash data. Common routines.
+ *
+ * Copyright (C) 2020 Thibaut VARÈNE <hacks+kernel@slashdirt.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ */
+
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/sysfs.h>
+
+#include "routerboot.h"
+
+static struct kobject *rb_kobj;
+
+/**
+ * routerboot_tag_find() - Locate a given tag in routerboot config data.
+ * @bufhead: the buffer to look into. Must start with a tag node.
+ * @buflen: size of bufhead
+ * @tag_id: the tag identifier to look for
+ * @pld_ofs: will be updated with tag payload offset in bufhead, if tag found
+ * @pld_len: will be updated with tag payload size, if tag found
+ *
+ * This incarnation of tag_find() does only that: it finds a specific routerboot
+ * tag node in the input buffer. Routerboot tag nodes are u32 values:
+ * - The low nibble is the tag identification number,
+ * - The high nibble is the tag payload length (node excluded) in bytes.
+ * The payload immediately follows the tag node. Tag nodes are 32bit-aligned.
+ * The returned pld_ofs will always be aligned. pld_len may not end on 32bit
+ * boundary (the only known case is when parsing ERD data).
+ * The nodes are cpu-endian on the flash media. The payload is cpu-endian when
+ * applicable. Tag nodes are not ordered (by ID) on flash.
+ *
+ * Return: 0 on success (tag found) or errno
+ */
+int routerboot_tag_find(const u8 *bufhead, const size_t buflen, const u16 tag_id,
+			u16 *pld_ofs, u16 *pld_len)
+{
+	const u32 *datum, *bufend;
+	u32 node;
+	u16 id, len;
+	int ret;
+
+	if (!bufhead || !tag_id)
+		return -EINVAL;
+
+	ret = -ENOENT;
+	datum = (const u32 *)bufhead;
+	bufend = (const u32 *)(bufhead + buflen);
+
+	while (datum < bufend) {
+		node = *datum++;
+
+		/* Tag list ends with null node */
+		if (!node)
+			break;
+
+		id = node & 0xFFFF;
+		len = node >> 16;
+
+		if (tag_id == id) {
+			if (datum >= bufend)
+				break;
+
+			if (pld_ofs)
+				*pld_ofs = (u16)((u8 *)datum - bufhead);
+			if (pld_len)
+				*pld_len = len;
+
+			ret = 0;
+			break;
+		}
+
+		/*
+		 * The only known situation where len may not end on 32bit
+		 * boundary is within ERD data. Since we're only extracting
+		 * one tag (the first and only one) from that data, we should
+		 * never need to forcefully ALIGN(). Do it anyway, this is not a
+		 * performance path.
+		 */
+		len = ALIGN(len, sizeof(*datum));
+		datum += len / sizeof(*datum);
+	}
+
+	return ret;
+}
+
+/**
+ * routerboot_rle_decode() - Simple RLE (MikroTik variant) decoding routine.
+ * @in: input buffer to decode
+ * @inlen: size of in
+ * @out: output buffer to write decoded data to
+ * @outlen: pointer to out size when function is called, will be updated with
+ * size of decoded output on return
+ *
+ * MikroTik's variant of RLE operates as follows, considering a signed run byte:
+ * - positive run => classic RLE
+ * - negative run => the next -<run> bytes must be copied verbatim
+ * The API is matched to the lzo1x routines for convenience.
+ *
+ * NB: The output buffer cannot overlap with the input buffer.
+ *
+ * Return: 0 on success or errno
+ */
+int routerboot_rle_decode(const u8 *in, size_t inlen, u8 *out, size_t *outlen)
+{
+	int ret, run, nbytes;	// use native types for speed
+	u8 byte;
+
+	if (!in || (inlen < 2) || !out)
+		return -EINVAL;
+
+	ret = -ENOSPC;
+	nbytes = 0;
+	while (inlen >= 2) {
+		run = *in++;
+		inlen--;
+
+		/* Verbatim copies */
+		if (run & 0x80) {
+			/* Invert run byte sign */
+			run = ~run & 0xFF;
+			run++;
+
+			if (run > inlen)
+				goto fail;
+
+			inlen -= run;
+
+			nbytes += run;
+			if (nbytes > *outlen)
+				goto fail;
+
+			/* Basic memcpy */
+			while (run-- > 0)
+				*out++ = *in++;
+		}
+		/* Stream of half-words RLE: <run><byte>. run == 0 is ignored */
+		else {
+			byte = *in++;
+			inlen--;
+
+			nbytes += run;
+			if (nbytes > *outlen)
+				goto fail;
+
+			while (run-- > 0)
+				*out++ = byte;
+		}
+	}
+
+	ret = 0;
+fail:
+	*outlen = nbytes;
+	return ret;
+}
+
+static int __init routerboot_init(void)
+{
+	rb_kobj = kobject_create_and_add("mikrotik", firmware_kobj);
+	if (!rb_kobj)
+		return -ENOMEM;
+
+	return rb_hardconfig_init(rb_kobj);
+}
+
+static void __exit routerboot_exit(void)
+{
+	rb_hardconfig_exit();
+	kobject_put(rb_kobj);	// recursive afaict
+}
+
+module_init(routerboot_init);
+module_exit(routerboot_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("MikroTik RouterBoot sysfs support");
+MODULE_AUTHOR("Thibaut VARENE");