[U-Boot] SPI NOR controller with direct mapping support

Hello Jagan,

I have a SoC which has a portion of memory where we can map a SPI NOR portion to do direct accesses. This is only for reading requests, otherwise regular SPI transfers must be used.

While there is no real support for spi-mem in spi-flash, what is the right way to implement a driver for such controller? It is more a SPI controller driver and should probably inherit from UCLASS_SPI. But inside the driver, it looks like we must access the spi_flash structure. Also, we would make use of functions like spi_flash_std_xxx from drivers/mtd/spi/ while I would definitely put the driver itself in drivers/spi/. Can you please comment on all these points?

Thanks, Miquèl