[PATCH] ARM: V6 MPCore v6_dma_inv_range RWFO fix

[Catalin Marinas]

On 24 November 2010 15:10, George G. Davis <gdavis at mvista.com> wrote:
> On Wed, Nov 24, 2010 at 10:42:13AM +0000, Catalin Marinas wrote:
>> On Tue, 2010-11-23 at 22:42 +0000, Russell King - ARM Linux wrote:
>> > On Wed, Nov 24, 2010 at 01:28:06AM +0300, Valentine Barshak wrote:
>> > > Cache ownership must be acqired by reading/writing data from the
>> > > cache line to make cache operation have the desired effect on the
>> > > SMP MPCore CPU. However, the ownership is never aquired in the
>> > > v6_dma_inv_range function when cleaning the first line and
>> > > flushing the last one, in case the address is not aligned
>> > > to D_CACHE_LINE_SIZE boundary.
>> > > Fix this by reading/writing data if needed, before performing
>> > > cache operations.
>> >
>> > You should do this on the data _inside_ the requested buffer.  We don't
>> > know if the overlapping cache line shares itself with some atomic
>> > variable, and doing a read-write on it could undo other updates to it.
>>
>> We could just use the boundary addresses to avoid writing beyond the
>> buffer. Something like below (pretty much moving the BIC after the RFO,
>> untested):
>>
>>
>> diff --git a/arch/arm/mm/cache-v6.S b/arch/arm/mm/cache-v6.S
>> index 99fa688..d63bb55 100644
>> --- a/arch/arm/mm/cache-v6.S
>> +++ b/arch/arm/mm/cache-v6.S
>> @@ -204,6 +204,10 @@ ENTRY(v6_flush_kern_dcache_area)
>>   */
>>  v6_dma_inv_range:
>>       tst     r0, #D_CACHE_LINE_SIZE - 1
>> +#ifdef CONFIG_DMA_CACHE_RWFO
>> +     ldrne   r2, [r0]                        @ read for ownership
>> +     strne   r2, [r0]                        @ write for ownership
>
> My concern doing RWFO prior to aligning "start" is that it could be
> non-word-aligned which may result in an alignment fault.

True. Maybe you can use ldrbne/strbne.

-- 
Catalin