Re: [PATCH 1/2] regmap: allow busses to request formatting with specific endianness

[Stephen Warren <swarren@wwwdotorg.org>]

On 05/23/2012 05:16 PM, Mark Brown wrote:
> On Wed, May 23, 2012 at 04:33:53PM -0600, Stephen Warren wrote:
> 
>> I'm not 100% sure if this is the approach you had in mind.
>> However, anything more all-encompassing would require separating
>> the concepts of endianness and
> 
> I wouldn't do this on the bus in the first instance, I'd do it on
> the device - it's pretty much orthogonal to the bus what the device
> wants and it's perfectly plausible that a device on another bus
> might've made unusual endiannness choices.  Otherwise it's pretty
> much what I was thinking of.
> 
> For MMIO I'd expect that a large proportion of devices on platform
> buses would pick native endianness.

I did briefly consider making this a property of regmap_config rather
than regmap_bus, but as you say, it'd mean every MMIO user would have
to specify the endianness value.

Also, it doesn't seem right for a device to be able to specify
register formatting endianness for MMIO; presumably we'd always want
that native.

Perhaps the solution is to have two fields; one for address formatting
(the endianness of which regmap-mmio.c will error-check is "native",
like it error-checks other fields) and a second for value
formatting/parsing, which I can see a device might want to influence
(e.g. to fix a byte swap in HW).

I suppose we could avoid every device having to specify the endianness
by introducing a fourth "DEFAULT" value == 0, and having the bus
define what default means - that way, I wouldn't have to edit any
drivers due to adding the regmap_bus field.

>> serialization that are coupled together in functions like 
>> regmap_format_4_12_write, and I'm not sure how that would work
>> conceptually.
> 
> Anything using format_write() can be ignored, it's already lost
> large chunks of functionality just from that.  Non-integer byte
> sizes cause issues.