cxl/mem: Add a debugfs version of 'iomem' for DPA, 'dpamem'

Dump the device-physical-address map for a CXL expander in /proc/iomem
style format. E.g.:

  cat /sys/kernel/debug/cxl/mem1/dpamem
  00000000-0fffffff : ram
  10000000-1fffffff : pmem
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165603885318.551046.8308248564880066726.stgit@dwillia2-xfhSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/hdm.c

 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2022 Intel Corporation. All rights reserved. */
 #include <linux/io-64-nonatomic-hi-lo.h>
+#include <linux/seq_file.h>
 #include <linux/device.h>
 #include <linux/delay.h>
 
@@ -16,6 +17,8 @@
  * for enumerating these registers and capabilities.
  */
 
+static DECLARE_RWSEM(cxl_dpa_rwsem);
+
 static int add_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
 			   int *target_map)
 {
@@ -128,6 +131,28 @@ struct cxl_hdm *devm_cxl_setup_hdm(struct cxl_port *port)
 }
 EXPORT_SYMBOL_NS_GPL(devm_cxl_setup_hdm, CXL);
 
+static void __cxl_dpa_debug(struct seq_file *file, struct resource *r, int depth)
+{
+	unsigned long long start = r->start, end = r->end;
+
+	seq_printf(file, "%*s%08llx-%08llx : %s\n", depth * 2, "", start, end,
+		   r->name);
+}
+
+void cxl_dpa_debug(struct seq_file *file, struct cxl_dev_state *cxlds)
+{
+	struct resource *p1, *p2;
+
+	down_read(&cxl_dpa_rwsem);
+	for (p1 = cxlds->dpa_res.child; p1; p1 = p1->sibling) {
+		__cxl_dpa_debug(file, p1, 0);
+		for (p2 = p1->child; p2; p2 = p2->sibling)
+			__cxl_dpa_debug(file, p2, 1);
+	}
+	up_read(&cxl_dpa_rwsem);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_dpa_debug, CXL);
+
 static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
 			    int *target_map, void __iomem *hdm, int which)
 {

drivers/cxl/core/port.c

@@ -1506,6 +1506,7 @@ struct dentry *cxl_debugfs_create_dir(const char *dir)
 {
 	return debugfs_create_dir(dir, cxl_debugfs);
 }
+EXPORT_SYMBOL_NS_GPL(cxl_debugfs_create_dir, CXL);
 
 static __init int cxl_core_init(void)
 {

drivers/cxl/cxlmem.h

@@ -372,4 +372,8 @@ struct cxl_hdm {
 	unsigned int interleave_mask;
 	struct cxl_port *port;
 };
+
+struct seq_file;
+struct dentry *cxl_debugfs_create_dir(const char *dir);
+void cxl_dpa_debug(struct seq_file *file, struct cxl_dev_state *cxlds);
 #endif /* __CXL_MEM_H__ */

drivers/cxl/mem.c

 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2022 Intel Corporation. All rights reserved. */
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/pci.h>
@@ -56,10 +57,26 @@ static void enable_suspend(void *data)
 	cxl_mem_active_dec();
 }
 
+static void remove_debugfs(void *dentry)
+{
+	debugfs_remove_recursive(dentry);
+}
+
+static int cxl_mem_dpa_show(struct seq_file *file, void *data)
+{
+	struct device *dev = file->private;
+	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
+
+	cxl_dpa_debug(file, cxlmd->cxlds);
+
+	return 0;
+}
+
 static int cxl_mem_probe(struct device *dev)
 {
 	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
 	struct cxl_port *parent_port;
+	struct dentry *dentry;
 	int rc;
 
 	/*
@@ -73,6 +90,12 @@ static int cxl_mem_probe(struct device *dev)
 	if (work_pending(&cxlmd->detach_work))
 		return -EBUSY;
 
+	dentry = cxl_debugfs_create_dir(dev_name(dev));
+	debugfs_create_devm_seqfile(dev, "dpamem", dentry, cxl_mem_dpa_show);
+	rc = devm_add_action_or_reset(dev, remove_debugfs, dentry);
+	if (rc)
+		return rc;
+
 	rc = devm_cxl_enumerate_ports(cxlmd);
 	if (rc)
 		return rc;