[PATCH] mtd: spi-nor: core: Check read CR support

[Jakub Czapiga <czapiga@google.com>]

Some SPI controllers like Intel's one on the PCI bus do not support
opcode 35h. This opcode is used to read the Configuration Register on
SPI-NOR chips that have 16-bit Status Register configured regardless
of the controller support for it. Adding a check call in the setup step
allows disabling use of the 35h opcode and falling back to the manual
Status Registers management.

Before:
openat(AT_FDCWD, "/dev/mtd0", O_RDWR)   = 4
ioctl(4, MIXER_WRITE(6) or MEMUNLOCK, {start=0, length=0x2000000}) = -1
EOPNOTSUPP

After:
openat(AT_FDCWD, "/dev/mtd0", O_RDWR)   = 4
ioctl(4, MIXER_WRITE(6) or MEMUNLOCK, {start=0, length=0x2000000}) = 0
ioctl(4, MIXER_WRITE(5) or MEMLOCK, {start=0x1800000, length=0x800000}) = 0

Suggested-by: Adeel Arshad <adeel.arshad@intel.com>
Signed-off-by: Jakub Czapiga <czapiga@google.com>
---
 drivers/mtd/spi-nor/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index ac4b960101cc..79deee3a50d3 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2608,6 +2608,10 @@ static int spi_nor_setup(struct spi_nor *nor,
 		}
 	}
 
+	/* Some SPI controllers might not support CR read opcode. */
+	if (spi_nor_read_cr(nor, nor->bouncebuf) == -EOPNOTSUPP)
+		nor->flags |= SNOR_F_NO_READ_CR;
+
 	/* Select the (Fast) Read command. */
 	err = spi_nor_select_read(nor, shared_mask);
 	if (err) {
-- 
2.51.0.384.g4c02a37b29-goog