[U-Boot] [RFC PATCH 00/20] SPI-NAND support

[Tom Rini]

On Mon, Jun 25, 2018 at 04:46:56PM +0200, Boris Brezillon wrote:
> On Mon, 25 Jun 2018 19:58:37 +0530
> Jagan Teki <jagan at amarulasolutions.com> wrote:
> 
> > >>> - convert fsl-qspi to spi-mem  
> > >>
> > >> We're not targeting the fsl-qspi controller here but a simple SPI
> > >> controller that is already upstreamed. But yes, the fsl-qspi driver
> > >> will have to be patched to support the spi-mem interface at some point.  
> > >
> > > Can you point me that simple spi-mem controller driver?
> 
> It's not a controller that implements spi-mem operations but a simple
> SPI controller (one that knows how to do regular SPI transfers and
> nothing more). But the spi-mem layer knows how to send spi_mem_op using
> regular transfer and that's why it works without any modification at
> the driver level.
> 
> 
> > >>>
> > >>> For spi-nor interface design, we have an example code here[2]
> > >>>
> > >>> I've paused this [2] series because of dm conversion of spi-drivers
> > >>> otherwise I need add legacy code like mmc-legacy.c, so if we really
> > >>> move to spi-mem design and okay with above design. I will try to move
> > >>> the current spi flash to add MTD driver-model so-that we can add
> > >>> spi-mem, spi-nand on top of it or we can work together to convert them
> > >>> all.  
> > >>
> > >> Why can't we do things iteratively. I mean, if the long term goal is to
> > >> convert everything to the driver model, then this patchset is going in
> > >> the right direction:
> > >>  - addition of DM helpers to the MTD_UCLASS
> > >>  - addition of the spi-mem interface properly integrated in the DM
> > >>    model of the SPI framework
> > >>  - addition of a SPI NAND driver, again properly integrated in the DM
> > >>  - integration of DM-ready MTD drivers and old MTD drivers in a single
> > >>    view exposed by the cmd/mtd.c command set
> > >>
> > >> I'd really like to limit the scope of this development to these topics,
> > >> which doesn't prevent you from converting other part of u-boot to the
> > >> spi-mem approach (SPI NOR is one example).
> > >>
> > >> I hope you understand our concerns and the fact that what you're asking
> > >> us to do as a dependency of getting SPI NAND support + cmd/mtd.c merged
> > >> is way more than we can actually provide.  
> > >
> > > To answer all these questions, I think we need to decide whether we go
> > > for MTD dm abstraction or existing MTD layer.
> > >
> > > When I say MTD dm abstraction, all mtd operation prototypes are in the
> > > form of udevice unlike existing MTD has mtd_info. when I initially
> > > supporting spi-nor (during Linux early spi-nor) I've reused existing
> > > MTD and written something like what Miquel did using mtd_info ops [3].
> > > but then developers on ML, proposed the new drivers should be form of
> > > driver-model abstraction, so I've added mtd driver model ops [4].
> > >
> > > I understand the new MTD dm abstraction in U-Boot is not possible for
> > > direct syncing from Linux, but we really want the u-boot way of
> > > handling drivers and trying to copy code from Linux by removing
> > > __UBOOT__ or any Linux specific macros. Since this is pretty much big
> > > task, ie the reason I'm asking for single driver from each MTD device
> > > so-that once the clear stack is ready other drivers can convert
> > > one-by-one.
> 
> I think I have to repeat my previous statement here. It would be very
> unfortunate if u-boot decides to take this direction (see Richard's
> reply), especially since I see absolutely no benefit in doing what you
> suggest. Having MTD devices registered to the uboot DM is something I
> can understand, deciding to no longer support the standard MTD API is
> something I don't.

I agree.  We want U-Boot to be able to leverage as much as possible from
the Linux kernel with as little re-working as possible.

-- 
Tom
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