mtd: phram: Allow cached mappings

Currently phram always uses ioremap(), but this is unnecessary when
normal memory is used.  If the reserved-memory node does not specify the
no-map property, indicating it should be mapped as system RAM and
ioremap() cannot be used on it, use a cached mapping using
memremap(MEMREMAP_WB) instead.

On one of my systems this improves read performance by ~70%.

(Note that this driver has always used normal memcpy/memset functions on
memory obtained from ioremap(), which sparse doesn't like.  There is no
memremap() variant which maps exactly to ioremap() on all architectures,
so that behaviour of the driver is not changed to avoid affecting
existing users, but the sparse warnings are suppressed in the moved code
with __force.)
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220510151822.1809278-1-vincent.whitchurch@axis.com

drivers/mtd/devices/phram.c

@@ -34,6 +34,7 @@
 struct phram_mtd_list {
 	struct mtd_info mtd;
 	struct list_head list;
+	bool cached;
 };
 
 static LIST_HEAD(phram_list);
@@ -80,13 +81,41 @@ static int phram_write(struct mtd_info *mtd, loff_t to, size_t len,
 	return 0;
 }
 
+static int phram_map(struct phram_mtd_list *phram, phys_addr_t start, size_t len)
+{
+	void *addr = NULL;
+
+	if (phram->cached)
+		addr = memremap(start, len, MEMREMAP_WB);
+	else
+		addr = (void __force *)ioremap(start, len);
+	if (!addr)
+		return -EIO;
+
+	phram->mtd.priv = addr;
+
+	return 0;
+}
+
+static void phram_unmap(struct phram_mtd_list *phram)
+{
+	void *addr = phram->mtd.priv;
+
+	if (phram->cached) {
+		memunmap(addr);
+		return;
+	}
+
+	iounmap((void __iomem *)addr);
+}
+
 static void unregister_devices(void)
 {
 	struct phram_mtd_list *this, *safe;
 
 	list_for_each_entry_safe(this, safe, &phram_list, list) {
 		mtd_device_unregister(&this->mtd);
-		iounmap(this->mtd.priv);
+		phram_unmap(this);
 		kfree(this->mtd.name);
 		kfree(this);
 	}
@@ -96,6 +125,7 @@ static int register_device(struct platform_device *pdev, const char *name,
 			   phys_addr_t start, size_t len, uint32_t erasesize)
 {
 	struct device_node *np = pdev ? pdev->dev.of_node : NULL;
+	bool cached = np ? !of_property_read_bool(np, "no-map") : false;
 	struct phram_mtd_list *new;
 	int ret = -ENOMEM;
 
@@ -103,9 +133,10 @@ static int register_device(struct platform_device *pdev, const char *name,
 	if (!new)
 		goto out0;
 
-	ret = -EIO;
-	new->mtd.priv = ioremap(start, len);
-	if (!new->mtd.priv) {
+	new->cached = cached;
+
+	ret = phram_map(new, start, len);
+	if (ret) {
 		pr_err("ioremap failed\n");
 		goto out1;
 	}
@@ -140,7 +171,7 @@ static int register_device(struct platform_device *pdev, const char *name,
 	return 0;
 
 out2:
-	iounmap(new->mtd.priv);
+	phram_unmap(new);
 out1:
 	kfree(new);
 out0:
@@ -362,7 +393,7 @@ static int phram_remove(struct platform_device *pdev)
 	struct phram_mtd_list *phram = platform_get_drvdata(pdev);
 
 	mtd_device_unregister(&phram->mtd);
-	iounmap(phram->mtd.priv);
+	phram_unmap(phram);
 	kfree(phram);
 
 	return 0;