[PATCH v2] mtd: Fix mtd not the same name not registered if nvmem

[Ricardo Ribalda Delgado]

When the nvmem framework is enabled, a nvmem device is created per mtd
device/partition.

It is not uncommon that a device can have multiple mtd devices with
partitions that have the same name. Eg, when there DT overlay is allowed
and the same device with mtd is attached twice.

Under that circumstances, the mtd fails to register due to a name
duplication on the nvmem framework.

With this patch we add a _1, _2, _X to the subsequent names if there is
a collition, and throw a warning, instead of not starting the mtd
device.

[    8.948991] sysfs: cannot create duplicate filename '/bus/nvmem/devices/Production Data'
[    8.948992] CPU: 7 PID: 246 Comm: systemd-udevd Not tainted 5.5.0-qtec-standard #13
[    8.948993] Hardware name: AMD Dibbler/Dibbler, BIOS 05.22.04.0019 10/26/2019
[    8.948994] Call Trace:
[    8.948996]  dump_stack+0x50/0x70
[    8.948998]  sysfs_warn_dup.cold+0x17/0x2d
[    8.949000]  sysfs_do_create_link_sd.isra.0+0xc2/0xd0
[    8.949002]  bus_add_device+0x74/0x140
[    8.949004]  device_add+0x34b/0x850
[    8.949006]  nvmem_register.part.0+0x1bf/0x640
...
[    8.948926] mtd mtd8: Failed to register NVMEM device

Signed-off-by: Ricardo Ribalda Delgado <ribalda@xxxxxxxxxx>
---
v2: I left behind on my patch a 

mtd->nvmem = NULL;

from my tests. Sorry.

 drivers/mtd/mtdcore.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 5fac4355b9c2..7a4b520ef3b0 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -28,6 +28,7 @@
 #include <linux/leds.h>
 #include <linux/debugfs.h>
 #include <linux/nvmem-provider.h>
+#include <linux/nvmem-consumer.h>
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/partitions.h>
@@ -545,13 +546,34 @@ static int mtd_nvmem_reg_read(void *priv, unsigned int offset,
 	return retlen == bytes ? 0 : -EIO;
 }
 
+static int nvmem_next_name(const char *init_name, char *name, size_t len)
+{
+	unsigned int i = 0;
+	int ret = 0;
+	struct nvmem_device *dev = NULL;
+
+	strlcpy(name, init_name, len);
+
+	while ((ret < len) &&
+	       !IS_ERR(dev = nvmem_device_find(name, device_match_name))) {
+		nvmem_device_put(dev);
+		ret = snprintf(name, len, "%s_%u", init_name, ++i);
+	}
+
+	if (ret >= len)
+		return -ENOMEM;
+
+	return i;
+}
+
 static int mtd_nvmem_add(struct mtd_info *mtd)
 {
 	struct nvmem_config config = {};
+	char name[128];
+	int ret = 0;
 
 	config.id = -1;
 	config.dev = &mtd->dev;
-	config.name = mtd->name;
 	config.owner = THIS_MODULE;
 	config.reg_read = mtd_nvmem_reg_read;
 	config.size = mtd->size;
@@ -562,6 +584,13 @@ static int mtd_nvmem_add(struct mtd_info *mtd)
 	config.no_of_node = true;
 	config.priv = mtd;
 
+	if (mtd->name) {
+		ret = nvmem_next_name(mtd->name, name, sizeof(name));
+		if (ret < 0)
+			return ret;
+		config.name = name;
+	}
+
 	mtd->nvmem = nvmem_register(&config);
 	if (IS_ERR(mtd->nvmem)) {
 		/* Just ignore if there is no NVMEM support in the kernel */
@@ -573,6 +602,10 @@ static int mtd_nvmem_add(struct mtd_info *mtd)
 		}
 	}
 
+	if (ret)
+		dev_warn(&mtd->dev, "mtdev %s renamed to %s due to name collision",
+				mtd->name, nvmem_dev_name(mtd->nvmem));
+
 	return 0;
 }
 
-- 
2.25.1