Octal RAM driver support related query

[Vignesh Raghavendra]

Hi Priyank,

+Tudor,

On 06/07/20 11:57 am, Miquel Raynal wrote:
> Hi Priyank,
> 
> +mtd maintainers
> +mtd list
> 
> Priyank Bhatt <priyankbhatt196 at gmail.com> wrote on Mon, 6 Jul 2020
> 11:05:14 +0530:
> 
>> Hi Miquel,
>>
>> I am working on NXP's iMX8 and trying to communicate to an ISSI Octal RAM with its flexSPI interface. I was recently going through a presentation *MTD: What's new? *from www.bootlin.com and at the end I found that in what's next section you have listed hyperRAM support.
>>
>> So my question: Is there any OctalRAM supported driver which I can refer to create my own for a specific chip manufacturer?
>> Right now I am referring mchp23k256.c(microchip) SPI RAM driver inside /driver/mtd/devices. But I am a little confused as to how to use my driver in Octal mode.
> 
> I guess we should ask Vignesh about it because he is the one mastering
> this subsystem, I could only give you dump answers about these devices
> :)
> 

There is no support for any type of Octal RAM devices currently.

Also HyperRAM and Octal RAM use different protocols... Octal RAM uses
traditional (Octal) SPI command set where as HyperRAM uses HyperBus
protocol (https://www.cypress.com/products/hyperram-memory). Even ISSI
website lists Octal and HyperRAM as two different products

Traditionally RAM devices that follow SPI NOR protocol have been
supported under drivers/mtd/spi-nor/  (Eg.: cy15x104q, mr25h* and
mb85rs1mt). Read/write logic in drivers/mtd/spi-nor/core.c has been
sufficient enough to handle these RAM devices as well.

I don't have access to ISSI Octal RAM datasheets, but if these RAM
devices use same commandset as SPI/Octal SPI NOR flashes then we can
continue to support them under SPI NOR framework.

Otherwise, there would be a need for separate Octal RAM driver under
drivers/mtd/devices/ which would then use spi_mem_ops to communicate
with spi-nxp-fspi.c driver (just like drivers/mtd/spi-nor/core.c)

Please note that SPI NOR framework still lacks complete Octal mode
support.. There is a patchset to add 8D-8D-8D mode Octal SPI NOR flash
that still under review:

https://patchwork.ozlabs.org/project/linux-mtd/list/?series=185337

This patchset might be prerequisite to support Octal RAM under SPI NOR
framework

Regards
Vignesh