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

[Miquel Raynal <miquel.raynal@bootlin.com>]

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