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Brian Norris authored
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>
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