1 files changed, 111 insertions, 0 deletions
diff --git a/src/libcamera/sysfs.cpp b/src/libcamera/sysfs.cpp
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+++ b/src/libcamera/sysfs.cpp
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+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * Miscellaneous utility functions to access sysfs
+ */
+
+#include "libcamera/internal/sysfs.h"
+
+#include <fstream>
+#include <sstream>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+
+#include <libcamera/base/file.h>
+#include <libcamera/base/log.h>
+
+/**
+ * \file sysfs.h
+ * \brief Miscellaneous utility functions to access sysfs
+ */
+
+namespace libcamera {
+
+LOG_DEFINE_CATEGORY(SysFs)
+
+namespace sysfs {
+
+/**
+ * \brief Retrieve the sysfs path for a character device
+ * \param[in] deviceNode Path to character device node
+ * \return The sysfs path on success or an empty string on failure
+ */
+std::string charDevPath(const std::string &deviceNode)
+{
+	struct stat st;
+	int ret = stat(deviceNode.c_str(), &st);
+	if (ret < 0) {
+		ret = -errno;
+		LOG(SysFs, Error)
+			<< "Unable to stat '" << deviceNode << "': "
+			<< strerror(-ret);
+		return {};
+	}
+
+	std::ostringstream dev("/sys/dev/char/", std::ios_base::ate);
+	dev << major(st.st_rdev) << ":" << minor(st.st_rdev);
+
+	return dev.str();
+}
+
+/**
+ * \brief Retrieve the path of the firmware node for a device
+ * \param[in] device Path in sysfs to search
+ *
+ * Physical devices in a system are described by the system firmware. Depending
+ * on the type of platform, devices are identified using different naming
+ * schemes. The Linux kernel abstract those differences with "firmware nodes".
+ * This function retrieves the firmware node path corresponding to the
+ * \a device.
+ *
+ * For DT-based systems, the path is the full name of the DT node that
+ * represents the device. For ACPI-based systems, the path is the absolute
+ * namespace path to the ACPI object that represents the device. In both cases,
+ * the path is guaranteed to be unique and persistent as long as the system
+ * firmware is not modified.
+ *
+ * \return The firmware node path on success or an empty string on failure
+ */
+std::string firmwareNodePath(const std::string &device)
+{
+	std::string fwPath, node;
+	struct stat st;
+
+	/* Lookup for DT-based systems */
+	node = device + "/of_node";
+	if (!stat(node.c_str(), &st)) {
+		char *ofPath = realpath(node.c_str(), nullptr);
+		if (!ofPath)
+			return {};
+
+		static const char prefix[] = "/sys/firmware/devicetree";
+		if (strncmp(ofPath, prefix, strlen(prefix)) == 0)
+			fwPath = ofPath + strlen(prefix);
+		else
+			fwPath = ofPath;
+
+		free(ofPath);
+
+		return fwPath;
+	}
+
+	/* Lookup for ACPI-based systems */
+	node = device + "/firmware_node/path";
+	if (File::exists(node)) {
+		std::ifstream file(node);
+		if (!file.is_open())
+			return {};
+
+		std::getline(file, fwPath);
+		file.close();
+
+		return fwPath;
+	}
+
+	return {};
+}
+
+} /* namespace sysfs */
+
+} /* namespace libcamera */