mtd: spi-nor: add support to non-uniform SFDP SPI NOR flash memories
Based on Cyrille Pitchen's patch https://lkml.org/lkml/2017/3/22/935. This patch is a transitional patch in introducing the support of SFDP SPI memories with non-uniform erase sizes like Spansion s25fs512s. Non-uniform erase maps will be used later when initialized based on the SFDP data. Introduce the memory erase map which splits the memory array into one or many erase regions. Each erase region supports up to 4 erase types, as defined by the JEDEC JESD216B (SFDP) specification. To be backward compatible, the erase map of uniform SPI NOR flash memories is initialized so it contains only one erase region and this erase region supports only one erase command. Hence a single size is used to erase any sector/block of the memory. Besides, since the algorithm used to erase sectors on non-uniform SPI NOR flash memories is quite expensive, when possible, the erase map is tuned to come back to the uniform case. The 'erase with the best command, move forward and repeat' approach was suggested by Cristian Birsan in a brainstorm session, so: Suggested-by: NCristian Birsan <cristian.birsan@microchip.com> Signed-off-by: NTudor Ambarus <tudor.ambarus@microchip.com> Reviewed-by: NMarek Vasut <marek.vasut@gmail.com> Signed-off-by: NBoris Brezillon <boris.brezillon@bootlin.com>
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