Re: [PATCH] m68knommu: allow ColdFire CPUs to use unaligned accesses

[Philippe De Muyter <phdm@macqel.be>]

Hi Greg,

On Fri, Jun 08, 2012 at 10:19:43PM +1000, Greg Ungerer wrote:
> Hi Philippe,
>
> On 06/08/2012 08:39 PM, Philippe De Muyter wrote:
>> On Fri, Jun 08, 2012 at 03:43:00PM +1000, gerg@snapgear.com wrote:
>>> From: Greg Ungerer<gerg@uclinux.org>
>>>
>>> All current ColdFire CPUs are able to support unaligned memory accesses.
>>> So remove the CONFIG_CPU_HAS_NO_UNALIGNED option selection for ColdFire.
>>>
>>> It seems that the current restriction was inherrited from the early 
>>> non-MMU
>>> support for the basic 68000 proecssors - which do not support unaligned
>>> accesses.
>>
>> It seems that the first ColdFires needed the restriction :
>>
>> I read in the "MCF5200 ColdFire Family ProgrammerÆs Reference Manual" 
>> :
>>
>> The ColdFire processor default configuration supports word- and
>> longword-sized operand references on 0-modulo-2 and 0-modulo-4
>> addresses, respectively. All other references are defined as
>> misaligned accesses. Any attempt to access a misaligned operand
>> generates an address-error exception, unless the optional hardware
>> module for handling misalignment is present. This misalignment
>> module converts any misaligned operand references into a series
>> of aligned bus cycles to access the data. The existence of the
>> misalignment module is implementation-dependent and is documented
>> in the appropriate ColdFire userÆs manual.

I mentionned that only to make you able to soften the commit comment :)

>
> I wish Freescale really did make that clear within the doco for each
> part!
>
> The oldest (and I assume simplest) part we support is the 5206, and it
> does explicitly state in the MCF5206UM that it supports unaligned
> accesses (Section 6.6). It is not as clear as this in some of the
> other CPU/SoC User Manuals that I looked through.
>
> I am pretty confident that all the parts we currently support in Linux
> do unaligned accesses.

I agree.  And if some parts did not implement it, we'd see it quickly.

Regards

Philippe