OMAP3: Warning: swp{b} use is deprecated for this architecture

[Jean Pihet]

Hi Will,

On Thu, Dec 16, 2010 at 6:05 PM, Will Deacon <will.deacon at arm.com> wrote:
> Hi Jean,
>
>> >>> Here is the offending code excerpt:
>> >>>
>> >>> wait_sem:
>> >>>         mov     r0,#1
>> >>>         ldr     r1, sdrc_scratchpad_sem
>> >>> wait_loop:
>> >>>         ldr     r2, [r1]        @ load the lock value
>> >>>         cmp     r2, r0          @ is the lock free ?
>> >>>         beq     wait_loop       @ not free...
>> >>>         swp     r2, r0, [r1]    @ semaphore free so lock it and proceed
>> >>>         cmp     r2, r0          @ did we succeed ?
>> >>>         beq     wait_sem        @ no - try again
>> >>
>> >> (untested, as my LDP is useless because of OMAP regressions.)
>> >>
>> >> wait_sem:
>> >>        mov     r0, #1
>> >>        ldr     r1, sdrc_scratchpad_sem
>> >> wait_loop:
>> >>        ldrex   r2, [r1]        @ load lock value
>> >>        teq     r2, r0          @ is lock free ( != 1)
>> >>        beq     wait_loop       @ no, try again
>> >>        strex   r2, r0, [r1]    @ try to lock
>> >>        teq     r2, #0          @ did store succeed?
>> >>        bne     wait_loop       @ no, try again
>> >
>> > I'm not familiar with the OMAP code but I recall they needed swp for
>> > some synchronisation with external processor (DSP). Is this still the
>> > case?
>> This code is meant to be used by the new DVFS code which is not merged in yet.
>
> I don't know what you do with this lock held or what the contention
> is like, but you probably want a memory barrier immediately after you've
> acquired it and another one before you release it.
OK, thanks for the suggestion.

Since this code is not used at the moment it will be removed.
It shall be added back, fixed and tested later when the API will be in real use.

Thanks,
Jean

>
> Will
>
>
>
>
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