linux-kernel - Re: [PATCH v2] mtd: spi-nor: Add support for SPI boot flash access for AMD Family 16h

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Date:   Tue, 30 Oct 2018 09:26:05 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     "Grandbois, Brett" <brett.grandbois@...ngear.com>
Cc:     Marek Vasut <marek.vasut@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mtd: spi-nor: Add support for SPI boot flash access
 for AMD Family 16h

On Mon, 29 Oct 2018 23:15:42 +0000
"Grandbois, Brett" <brett.grandbois@...ngear.com> wrote:

> On 28/10/18 1:39 am, Boris Brezillon wrote:
> > Hi Brett,
> >
> > On Tue, 16 Oct 2018 00:57:41 +0000
> > "Grandbois, Brett"<brett.grandbois@...ngear.com>  wrote:
> >  
> >> Add support to expose the SPI boot flash on AMD Family 16h CPUs as
> >> a standard mtd device to give userspace BIOS updaters greater
> >> feature support.  The BIOS and Kernel Developer's Guide refers to
> >> this as the 'SPI ROM' controller and so the driver follows that
> >> naming convention for consistency.
> >>  
> > We're currently trying to convert spi-nor controller drivers to the
> > spi-mem interface [1]. Can you look at this new interface and tell
> > me if you'd be able to implement it? If that's not possible, then
> > I'd prefer to have this driver implement the mtd_info interface
> > directly.  
> 
> So from going over the spi-mem interface it looks like the intent is
> for these sorts of devices to be a standard spi_controller with only
> mem_ops defined and the transfer/_one/_one_message left as NULL?  Is
> that correct? 

Yes

> That's a bit of a pivot from how it's currently done
> (it's conceptually similar to the intel-spi-pci driver so I was
> following that)

Yes, and that's exactly what I'd like to avoid. intel-spi-pci will
probably be the trickiest conversion, so I'd like to avoid having
another one ;-).

> but I should be able to rework it to the new
> interface.  This then lives under drivers/spi and thus should be
> submitted to linux-spi? 

Actually, if the controller is only ever connected to the same SPI NOR
chip (no need for advanced detection scheme) and does not support
support Octo/Quad/Dual modes (or any other advanced features), you'll
be better off implementing mtd->_read/_write/_erase() directly (the
driver would then live in drivers/mtd/devices/).