[PATCH v3 0/7] mv643xx.c: Add basic device tree support.
ian.molton at codethink.co.uk
Thu Aug 9 11:21:27 EDT 2012
On 09/08/12 12:43, Arnd Bergmann wrote:
> On 08/08/12 14:19, Ian Molton wrote:
> > On 08/08/12 13:39, Arnd Bergmann wrote:
> >> On Wednesday 08 August 2012, Ian Molton wrote:
> >>> This method would require a small amount of rework in the driver to
> >>> set up <n> ports, rather than just one.
> >> This looks quite nice, but it is still very much incompatible with the
> >> existing binding. Obviously we can abandon an existing binding and
> >> introduce a second one for the same hardware, but that should not
> >> be taken lightly.
> > Fair, however the existing users aren't anywhere near as
> > numerous as the new ones.
> Depends on how you count the numbers. I see at least three machines
> supported in the kernel with the old binding and none with the new one
> so far ;-)
I'm curious as to how any of those actually work, given the
apparent total lack of a mv64360-mdio device binding...
> > As you can see, instead of putting port1 at +0x1700 or so,
> > marvell have overlapped the register files - in fact, doubly
> > so, since port1 + 0x1080 is right in the middle of
> > (port0 + 0x1000) -> (port0 + 0x16ff), so one cant simply map two
> > sets of regs like 0x0000->0x03ff and 0x1000->0x16ff for port one
> > either.
> This could theoretically be dealt with by having 5 register ranges
I make that three...
> per device, but that would cause extra overhead and also be
> incompatible with the existing binding.
> I think showing one
> parent device with children at address 0, 1 and 2 is ok.
Is it acceptable for the child devices to directly access the
parents register space? because there would be no other
way for that to work.
> The driver
> already knows all those offsets and they are always the same
> for all variants of mv643xx, right?
Yes, but its not clean. And no amount of refactoring is
really going to make a nice driver that also fits the ancient
(and badly thought out) OF bindings.
If we have to break things, we can at least go for a nice
clean design, surely?
The ports arent really child devices of the MAC. The MAC
just has 3 ports.
Luckily, it looks like the existing users don't actually use
the device tree to set up the driver at all, preferring to
translate their D-T bindings to calls to
platform_device_register() so all we'd need to do to
support them is completely ignore them.
We're going to have to maintain a legacy
platform_device -> DT bindings hack somewhere anyway,
at least until the remaining other users of the driver
convert to D-T.
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