mtd: m25p80: remove M25PXX_USE_FAST_READ Kconfig

Remove the compile-time option for FAST_READ, since we have run-time
support for detecting it. This refactors the logic for enabling
fast-read, such that for DT-enabled devices, we honor the
"m25p,fast-read" property but for non-DT devices, we default to using
FAST_READ whenever the flash device supports it.

Normal READ and FAST_READ differ only in the following:

  * FAST_READ supports SPI higher clock frequencies [1]

  * number of dummy cycles; FAST_READ requires 8 dummy cycles (whereas
    READ requires 0) to allow the flash sufficient setup time, even when
    running at higher clock speeds

Thus, for flash chips which support FAST_READ, there is otherwise no
limiting reason why we cannot use the FAST_READ opcode instead of READ.
It simply allows the SPI controller to run at higher clock rates. So
theoretically, nobody should be needing the compile-time option anyway.

  [1] I have a Spansion S25FL128S datasheet which says:

    "The maximum operating clock frequency for the READ command is 50
    MHz."

  And:

    "The maximum operating clock frequency for FAST READ command is 133
    MHz."

Signed-off-by: Brian Norris <computersforpeace@gmail.com>

1 files changed, 0 insertions, 7 deletions

diff --git a/drivers/mtd/devices/Kconfig b/drivers/mtd/devices/Kconfig
index 74ab4b7..0128138 100644
--- a/drivers/mtd/devices/Kconfig
+++ b/drivers/mtd/devices/Kconfig
@@ -95,13 +95,6 @@ config MTD_M25P80
 	  if you want to specify device partitioning or to use a device which
 	  doesn't support the JEDEC ID instruction.
 
-config M25PXX_USE_FAST_READ
-	bool "Use FAST_READ OPCode allowing SPI CLK >= 50MHz"
-	depends on MTD_M25P80
-	default y
-	help
-	  This option enables FAST_READ access supported by ST M25Pxx.
-
 config MTD_SPEAR_SMI
 	tristate "SPEAR MTD NOR Support through SMI controller"
 	depends on PLAT_SPEAR