Re: [PATCH RFT 0/2/2] mtd: hyperbus: add Renesas RPC-IF driver

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

On Wed, 19 Feb 2020 23:13:36 +0300
Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx> wrote:

> > One way would be to extend spi_mem_op to support above template along
> > with a new field to distinguish SPI NOR vs HyperFlash protocol. HyperBus
> > core can then register a spi_device and use spi-mem ops to talk to
> > controller driver.  
> 
>    We have discussed this idea with Mark Brown, the SPI maintainer, and
> he wasn't terribly impressed (I've invited him to #mtd -- his nick is
> broonie and mine is headless, I'm also adding him to CC:).
> 
> > So, I suggest making Renesas RPC-IF backend a full fledged spi-mem
> > driver (instead of driver/memory) and use extended spi_mem_op to support
> > HyperFlash.  
> 
>    I don't think cramming support for the different flash busses into
> the SPI drivers is a good idea...

That's what I thought at first (SPI and Hyperflash seemed different
enough to not merge them), then I had a look at Vignesh's HyperFlash
presentation [1], and there's one aspect that made me reconsider this
PoV. Slide 25 (xSPI compliant HyperFlash): having devices bouncing from
one driver to another depending on the mode they operate in is likely to
be painful to handle. Not to mention that Octo+DTR is similar to
HyperBus from an HW PoV (at the PHY level, they both have CS, CLK,
DQS/RWDS, DQ/IO[0:7] signals, only the protocol differs).

[1]https://elinux.org/images/3/38/HBMC-v1.pdf

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