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From: Felix Fietkau <nbd@nbd.name>
Date: Fri, 23 Feb 2018 17:12:16 +0100
Subject: [PATCH] mtd: m25p80: allow fallback from spi_flash_read to regular
 SPI transfer

Some flash controllers, e.g. on the ath79 platform can support a fast
flash read via memory mapping, but only if the flash chip is in
3-byte address mode.

Since spi_flash_read_supported does not have access to the same data as
spi_flash_read, the driver can't detect an unsupported call until m25p80
has decided to use spi_flash_read.

Allow the driver to indicate a fallback to a regular SPI transfer by
returning -EOPNOTSUPP

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---

--- a/drivers/mtd/devices/m25p80.c
+++ b/drivers/mtd/devices/m25p80.c
@@ -170,9 +170,11 @@ static ssize_t m25p80_read(struct spi_no
                msg.data_nbits = data_nbits;
 
                ret = spi_flash_read(spi, &msg);
-               if (ret < 0)
-                       return ret;
-               return msg.retlen;
+               if (ret != -EOPNOTSUPP) {
+                       if (ret < 0)
+                               return ret;
+                       return msg.retlen;
+               }
        }
 
        spi_message_init(&m);