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

[Greg Ungerer <gerg@snapgear.com>]

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 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.

Regards
Greg


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Greg Ungerer  --  Principal Engineer        EMAIL:     gerg@snapgear.com
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