devres: keep both device name and resource name in pretty name

Sometimes debugging a device is easiest using devmem on its register
map, and that can be seen with /proc/iomem. But some device drivers have
many memory regions. Take for example a networking switch. Its memory
map used to look like this in /proc/iomem:

1fc000000-1fc3fffff : pcie@1f0000000
  1fc000000-1fc3fffff : 0000:00:00.5
    1fc010000-1fc01ffff : sys
    1fc030000-1fc03ffff : rew
    1fc060000-1fc0603ff : s2
    1fc070000-1fc0701ff : devcpu_gcb
    1fc080000-1fc0800ff : qs
    1fc090000-1fc0900cb : ptp
    1fc100000-1fc10ffff : port0
    1fc110000-1fc11ffff : port1
    1fc120000-1fc12ffff : port2
    1fc130000-1fc13ffff : port3
    1fc140000-1fc14ffff : port4
    1fc150000-1fc15ffff : port5
    1fc200000-1fc21ffff : qsys
    1fc280000-1fc28ffff : ana

But after the patch in Fixes: was applied, the information is now
presented in a much more opaque way:

1fc000000-1fc3fffff : pcie@1f0000000
  1fc000000-1fc3fffff : 0000:00:00.5
    1fc010000-1fc01ffff : 0000:00:00.5
    1fc030000-1fc03ffff : 0000:00:00.5
    1fc060000-1fc0603ff : 0000:00:00.5
    1fc070000-1fc0701ff : 0000:00:00.5
    1fc080000-1fc0800ff : 0000:00:00.5
    1fc090000-1fc0900cb : 0000:00:00.5
    1fc100000-1fc10ffff : 0000:00:00.5
    1fc110000-1fc11ffff : 0000:00:00.5
    1fc120000-1fc12ffff : 0000:00:00.5
    1fc130000-1fc13ffff : 0000:00:00.5
    1fc140000-1fc14ffff : 0000:00:00.5
    1fc150000-1fc15ffff : 0000:00:00.5
    1fc200000-1fc21ffff : 0000:00:00.5
    1fc280000-1fc28ffff : 0000:00:00.5

That patch made a fair comment that /proc/iomem might be confusing when
it shows resources without an associated device, but we can do better
than just hide the resource name altogether. Namely, we can print the
device name _and_ the resource name. Like this:

1fc000000-1fc3fffff : pcie@1f0000000
  1fc000000-1fc3fffff : 0000:00:00.5
    1fc010000-1fc01ffff : 0000:00:00.5 sys
    1fc030000-1fc03ffff : 0000:00:00.5 rew
    1fc060000-1fc0603ff : 0000:00:00.5 s2
    1fc070000-1fc0701ff : 0000:00:00.5 devcpu_gcb
    1fc080000-1fc0800ff : 0000:00:00.5 qs
    1fc090000-1fc0900cb : 0000:00:00.5 ptp
    1fc100000-1fc10ffff : 0000:00:00.5 port0
    1fc110000-1fc11ffff : 0000:00:00.5 port1
    1fc120000-1fc12ffff : 0000:00:00.5 port2
    1fc130000-1fc13ffff : 0000:00:00.5 port3
    1fc140000-1fc14ffff : 0000:00:00.5 port4
    1fc150000-1fc15ffff : 0000:00:00.5 port5
    1fc200000-1fc21ffff : 0000:00:00.5 qsys
    1fc280000-1fc28ffff : 0000:00:00.5 ana

Fixes: 8d84b18f ("devres: always use dev_name() in devm_ioremap_resource()")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200601095826.1757621-1-olteanv@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

lib/devres.c

@@ -119,6 +119,7 @@ __devm_ioremap_resource(struct device *dev, const struct resource *res,
 {
 	resource_size_t size;
 	void __iomem *dest_ptr;
+	char *pretty_name;
 
 	BUG_ON(!dev);
 
@@ -129,7 +130,15 @@ __devm_ioremap_resource(struct device *dev, const struct resource *res,
 
 	size = resource_size(res);
 
-	if (!devm_request_mem_region(dev, res->start, size, dev_name(dev))) {
+	if (res->name)
+		pretty_name = devm_kasprintf(dev, GFP_KERNEL, "%s %s",
+					     dev_name(dev), res->name);
+	else
+		pretty_name = devm_kstrdup(dev, dev_name(dev), GFP_KERNEL);
+	if (!pretty_name)
+		return IOMEM_ERR_PTR(-ENOMEM);
+
+	if (!devm_request_mem_region(dev, res->start, size, pretty_name)) {
 		dev_err(dev, "can't request region for resource %pR\n", res);
 		return IOMEM_ERR_PTR(-EBUSY);
 	}