[RFC PATCH] mtd: spi-nor-core: Handle SPI_RX_SLOW in spi_nor_adjust_hwcaps()

[Bin Meng]

When CONFIG_SPI_FLASH_SMART_HWCAPS is on, SPI_RX_SLOW flag of the
SPI controller is not honored. This adds the missing logic there.

With this patch, SPI flash read works again with ICH SPI controller
on Intel Crown Bay board.

Signed-off-by: Bin Meng <bmeng.cn at gmail.com>

---
The quirky stuff of ICH SPI controller is that it only supports normal
read (opcode 3) but not fast read (opcode 11), so that's why SPI_RX_SLOW
was introduced before.

At present the ICH SPI driver does not implement the supports_op() hook.
I can add a check against opcode 11 there, however I see a comment in
spi_nor_check_op() saying that SPI controller implementation should not
check the opcode.

/*
 * First test with 4 address bytes. The opcode itself might be a 3B
 * addressing opcode but we don't care, because SPI controller
 * implementation should not check the opcode, but just the sequence.
 */

 drivers/mtd/spi/spi-nor-core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
index 99e2f16349..e9b46c39b5 100644
--- a/drivers/mtd/spi/spi-nor-core.c
+++ b/drivers/mtd/spi/spi-nor-core.c
@@ -2855,6 +2855,7 @@ spi_nor_adjust_hwcaps(struct spi_nor *nor,
 		      const struct spi_nor_flash_parameter *params,
 		      u32 *hwcaps)
 {
+	struct spi_slave *spi = nor->spi;
 	unsigned int cap;
 
 	/*
@@ -2879,6 +2880,10 @@ spi_nor_adjust_hwcaps(struct spi_nor *nor,
 		if (!(*hwcaps & BIT(cap)))
 			continue;
 
+		if ((spi->mode & SPI_RX_SLOW) &&
+		    (BIT(cap) == SNOR_HWCAPS_READ_FAST))
+			*hwcaps &= ~BIT(cap);
+
 		rdidx = spi_nor_hwcaps_read2cmd(BIT(cap));
 		if (rdidx >= 0 &&
 		    spi_nor_check_readop(nor, &params->reads[rdidx]))
-- 
2.25.1