[question] some question about the residue

[Russell King - ARM Linux]

On Mon, Nov 26, 2012 at 03:35:42PM +0800, Elen Song wrote:
> On 2012-11-26 14:49, Vinod Koul wrote:
>> On Mon, 2012-11-26 at 14:43 +0800, Elen Song wrote:
>>> Hi All:
>>>
>>> 	I got a question about the residue in struct dma_tx_state:
>>>
>>> 	I wonder what residue means, is it the current descriptor residue or
>>>
>>> 	the total dma buffer residue?
>> You read the status for descriptor, so it means this is residue for said
>> descriptor.
>>
>>
> Hi Koul:
>
> Well , I don't get it , if I read the status of a LLI, is it means the  
> residue of total LLI length?
>
> I saw driver/dma/amba-pl08x.c drivers/dma/coh901318.c, if read status of  
> a LLI, residue is the remain of LLI, not only
> current descriptor.
>
> 1 patch from Russel King how he realize device_tx_status said:
>
> [PATCH] ARM: PL08x: clean up LLI lookup
> As the LLI list is an array, we can use maths to locate which LLI
> index we're currently at, and then sum up the remaining LLI entries
> until we reach the end of the list.
>
> Is it right?

It is as far as fixing a pretty major bug in the driver, but it doesn't
fix the other bug in the driver where it sums up all outstanding
descriptors, which pre-dates the understanding of 'residue'.