Re: [PATCH v3 06/10] mtd: brcmstb_nand: add SoC-specific support

[Brian Norris <computersforpeace@gmail.com>]

On Fri, May 08, 2015 at 11:38:11PM +0200, Arnd Bergmann wrote:
> On Friday 08 May 2015 13:47:25 Brian Norris wrote:
> > On Fri, May 08, 2015 at 09:49:02PM +0200, Arnd Bergmann wrote:
> > > On Friday 08 May 2015 12:38:50 Brian Norris wrote:
> > > > On Fri, May 08, 2015 at 03:41:10PM +0200, Arnd Bergmann wrote:
> > > > > bcm63138_nand_driver with its own probe() function that calls the
> > > > > common probe function. That would make the soc specific parts
> > > > > better contained and match how we normally do abstractions of
> > > > > similar drivers.
> > > > 
> > > > OK, so I can imagine this might require changing the DT binding a bit [1]
> > > > (is that your goal?). But what's the intended software difference? [2]
> > > > I'll still be passing around the same sorts of callbacks from the
> > > > 'iproc_nand' probe to the common probe function.
> > 
> > ^^ before getting bogged down on the DT details (which can be changed
> > independently), I'd like to address this point.
> 
> The intended change is to make it work according to
> Documentation/driver-model/design-patterns.txt

Huh? There are two bullet points in that file, and neither are
particularly enlightening for this case. Maybe you're referring to your
mental design patterns documentation? :)

> basically, by having all the shared code be a "library" module that gets
> called by the actual hardware specific drivers, rather than having the
> shared code be the central driver that fans out into all possible subdrivers.

OK, I'll see what I can do. It will be a fairly opaque "library" though,
consisting largely of a single monolithic core driver. Might just move
to a whole drivers/mtd/nand/brcmnand/ subdirectory at the same time...

> > > Yes, I think this makes sense overall. Regarding the specific example, can you
> > > clarify how the register areas in iproc are structured?
> > > 
> > > The 0xf8105408 and 0x18046f00 start addresses are not aligned to large powers
> > > of two, which often indicates that they are part of some other, larger,
> > > unit that might need to have a driver of its own, so before we specify
> > > a binding like the one you proposed above I'd like to make sure we're not
> > > getting ourselves into trouble later.
> > 
> > I may want the Cygnus guys to speak up here, partly for technical
> > expertise and partly to know how much they care to share...
> > 
> > <0xf8105408 0x600>: covers a series of NAND_IDM registers. NAND has a
> > few bits we don't care about (for debugging, logging, and resetting), as
> > well as its interrupt enable bits. The adjacent blocks cover similar IDM
> > blocks for other cores (SPI, PNOR, DDR), and they are similarly
> > unaligned. Not sure why, exactly; probably just a compact layout.
> > 
> > <0x18046f00 0x20>: a series of 8 NAND interrupt registers, each word
> > containing a single bit representing status/clear. There is nothing
> > between the "nand" range and this range, and the SPI core register range
> > follows.
> > 
> > So I think these are pretty clearly-delineated register ranges for NAND,
> > and the alignment is not really missing anything. Adjacent hardware
> > (e.g., SPI) is independent, though pieces look similar. For one, it has
> > similar:
> > 
> >  * interrupt enable bits in the IDM range (0xf8106408 to 0xf8106a00);
> >    and
> >  * interrupt status/clear following the SPI block (0x180473a0 to
> >    0x180473b8)
> 
> This would in turn indicate that we should treat these ranges as
> an irqchip that handles all sorts of devices, but it really depends
> on the particular register layout.

OK, sure. But this has nothing to do with NAND (which we established
cannot be an irqchip on Cygnus). I think SPI is coming through the
pipeline soon, though, and that's a good point.

Brian