[PATCH 0/4] mtd: spi-nor: add a new framework for SPI NOR

[Brian Norris]

On Thu, Dec 05, 2013 at 02:35:47PM +0000, Angus Clark wrote:
> On 12/04/2013 06:44 PM, Brian Norris wrote:
> > On this topic, I have one more stick to throw on this fire; I have some
> > Broadcom hardware that consists of two pieces:
> > 
> >   (1) a true SPI controller, with single-line-I/O and
> >   (2) a Serial Flash controller that can accelerate flash read, using
> >       dual/quad I/O.
> 
> We support one platform with properties similar to the hardware you describe,
> and such a hybrid configuration was in mind when I was thinking about the
> spi-nor framework.  I am not sure how well this will come across over email, but
> I envisage something like this:
> 
>                              spi-nor
>                                 |
>                                 v
>                           [spi-nor-xfer]
>                                 |
>          ------------------------------------------------
>         |                       |                        |
>         v                       v                        v
>    spi-wrapper (<------)  hybrid-driver          serial-flash-driver
>         |                       |                        |
>       [SPI]                     |                        |
>         |                       |                        |
>         v                       |                        |
> generic-spi-driver              |                        |
>         |                       |                        |
>         v                       v                        v
> [generic-SPI-Cntrl]   [SPI-Flash-Read Cntrl]   [SPI-Flash-Controller]
> 
> The 'spi-nor' layer is responsible for Serial Flash domain knowledge, and how to
> generate 'spi-nor-xfer' messages.  The 'spi-wrapper' would provide an interface
> to the generic SPI framework, flattening the 'spi-nor-xfer' message to standard
> SPI calls.  The combination of 'spi-nor' and 'spi-wrapper' should achieve what
> we have today for the m25p80 driver.  The 'serial-flash-driver' in the example
> provides an implementation for a dedicated Serial Flash Controller, making use
> of the spi-nor-xfer semantics where required.  The 'hybrid-driver' could use the
> 'spi-wrapper' implementation for write and erase hooks, and optimised
> implementations for read hooks.

OK, that sounds reasonable. But how do I bind my "generic SPI driver"
with my "SPI NOR accelerated read driver" to represent this? Does the
hybrid driver (my accelerated-read driver) have to register itself as a
SPI protocol driver (struct spi_driver)? The "controller" boundaries
seem to get a little fuzzy under this design.

Brian