mtd: m25p80: allow arbitrary OF matching for "jedec,spi-nor"

When we added the "jedec,spi-nor" compatible string for use in this
driver, we added it as a modalias option. The modalias can be derived in
different ways for platform devices vs. device tree (of_*) matching. But
for device tree matching (the primary target of this identifier string),
the modalias is determined from the first entry in the 'compatible'
property. IOW, the following properties would bind to this driver:

	// Option (a), modalias = "spi-nor"
	compatible = "jedec,spi-nor";

	// Option (b), modalias = "spi-nor"
	compatible = "idontknowwhatimdoing,spi-nor";

But the following would not:

	// Option (c), modalias = "shinynewdevice"
	compatible = "myvendor,shinynewdevice", "jedec,spi-nor";

So, we'd like to match (a) and (c) (even when we don't have an explicit
entry for "shinynewdevice"), and we'd rather not allow (b).

To do this, we
  (1) always (for devices without specific platform data) pass the
      modalias to the spi-nor library;
  (2) rework the spi-nor library to not reject "bad" names, and
      instead just fall back to autodetection; and
  (3) add the .of_match_table to properly catch all "jedec,spi-nor".

This allows (a) and (c) without warnings, and rejects (b).
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/devices/m25p80.c

@@ -223,8 +223,6 @@ static int m25p_probe(struct spi_device *spi)
 	 */
 	if (data && data->type)
 		flash_name = data->type;
-	else if (!strcmp(spi->modalias, "spi-nor"))
-		flash_name = NULL; /* auto-detect */
 	else
 		flash_name = spi->modalias;
 
@@ -289,19 +287,25 @@ static const struct spi_device_id m25p_ids[] = {
 	{"m25p40-nonjedec"},	{"m25p80-nonjedec"},	{"m25p16-nonjedec"},
 	{"m25p32-nonjedec"},	{"m25p64-nonjedec"},	{"m25p128-nonjedec"},
 
-	/*
-	 * Generic support for SPI NOR that can be identified by the JEDEC READ
-	 * ID opcode (0x9F). Use this, if possible.
-	 */
-	{"spi-nor"},
 	{ },
 };
 MODULE_DEVICE_TABLE(spi, m25p_ids);
 
+static const struct of_device_id m25p_of_table[] = {
+	/*
+	 * Generic compatibility for SPI NOR that can be identified by the
+	 * JEDEC READ ID opcode (0x9F). Use this, if possible.
+	 */
+	{ .compatible = "jedec,spi-nor" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, m25p_of_table);
+
 static struct spi_driver m25p80_driver = {
 	.driver = {
 		.name	= "m25p80",
 		.owner	= THIS_MODULE,
+		.of_match_table = m25p_of_table,
 	},
 	.id_table	= m25p_ids,
 	.probe	= m25p_probe,

drivers/mtd/spi-nor/spi-nor.c

@@ -1015,11 +1015,11 @@ int spi_nor_scan(struct spi_nor *nor, const char *name, enum read_mode mode)
 	if (ret)
 		return ret;
 
-	/* Try to auto-detect if chip name wasn't specified */
-	if (!name)
-		id = spi_nor_read_id(nor);
-	else
+	if (name)
 		id = spi_nor_match_id(name);
+	/* Try to auto-detect if chip name wasn't specified or not found */
+	if (!id)
+		id = spi_nor_read_id(nor);
 	if (IS_ERR_OR_NULL(id))
 		return -ENOENT;