[U-Boot] [PATCH] ARM: mvebu: db-88f6820-amc: enable SPI_FLASH_BAR

[Vignesh Raghavendra]

On 02-Mar-19 5:02 PM, Stefan Roese wrote:
[...]
>>
>> It would be great if driver could be modified to support 3 and 4 byte
>> addressing modes.
> 
> I fail to see, what really is needed to make the SPI driver support
> 3 and 4 byte addressing modes. I recently added the MT7688 SPI
> driver (mt7621_spi.c) which supports 3 and 4 byte mode and I remember
> no driver specials that I needed to implement for this feature. Its
> address mode agnostic AFAICT and just xfers a buffer of data to and
> from the SPI device.
> 

Certain SPI controllers have special HW support to support SPI flashes
and therefore need knowledge of flash specific information such as
opcode, no. of address bytes etc. More details in this blog[1] Such
controllers should ideally use spi-mem interface like [2]
I see this line in kirkwood_spi.c[3] which seems to hard code address
bytes to 3? Can't really be sure w/o looking at the datasheet of SPI
controllers.

[1]
https://bootlin.com/blog/spi-mem-bringing-some-consistency-to-the-spi-memory-ecosystem/
[2] https://patchwork.ozlabs.org/patch/1039718/
[3]
https://elixir.bootlin.com/u-boot/latest/source/drivers/spi/kirkwood_spi.c#L132

> Could you please let me know, what exactly is missing for this 4 byte
> mode?
> 
> Thanks,
> Stefan
>