Re: [PATCH V3 5/7] serial: earlycon: Set UPIO_MEM32BE based on DT properties

[Peter Hurley <peter@hurleysoftware.com>]

Hi Kevin,

On 03/28/2015 03:28 PM, Kevin Cernekee wrote:
> On Sat, Mar 28, 2015 at 10:01 AM, Peter Hurley <peter@hurleysoftware.com> wrote:
>>>> I know these got ACKs already but as you point out in the commit log,
>>>> earlycon _will_ need reg-io-width, reg-offset and reg-shift. Since the
>>>> distinction between early_init_dt_scan_chosen_serial() and
>>>> of_setup_earlycon() is arbitrary, I'd rather see of_setup_earlycon()
>>>> taught to properly decode of_serial driver bindings instead of a
>>>> stack of parameters to of_setup_earlycon().
>>>>
>>>> In fact, this patch allows a mis-defined devicetree to bring up a
>>>> functioning earlycon because the 'big-endian' property is directly
>>>> associated with UPIO_MEM32BE, which will create incompatibility problems
>>>> when DT earlycon is fixed to decode the of_serial DT bindings.
>>>
>>> That's a good point. This hasn't been merged yet, so there isn't any
>>> impact on addressing this. I would propose that for consistency, the
>>> earlycon code should always default to 8-bit access. if big-endian
>>> accesses are required, then reg-io-width + big-endian must be specified.
>>>
>>> Something like the following would do it and would be future-proof. We
>>> can add support for 16 or 64bit big or little endian access if it ever
>>> became necessary.
>>
>> I was planning on adding MEM32BE support to OF earlycon on top of my
>> patch series 'OF earlycon cleanup', which adds full support for the
>> of_serial driver DT properties (among other things).
> 
> Hi Peter,
> 
> This is my latest work-in-progress, incorporating the feedback from
> you and Grant:
> 
> https://github.com/cernekee/linux/commits/endian
> 
> Not sure if this code plays nice with your recent cleanups?  If we're
> touching the same files/functions we should probably coordinate.

Ok, I'll look over your git tree and add whatever's required to
earlycon.

> Also, it is untested, as I do not currently have access to BE systems.
> If I get desperate I can try it on an LE system, adding the big-endian
> properties in DT and then hacking the 8250 driver to swap LE accesses
> for BE accesses.

Ok.

Regards,
Peter Hurley