Re: [PATCH v2 2/5] async_tx: Handle DMA devices having support for fewer PQ coefficients

[Anup Patel]

On Tue, Feb 7, 2017 at 1:57 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> On Tue, Feb 7, 2017 at 12:16 AM, Anup Patel <anup.patel@xxxxxxxxxxxx> wrote:
>> The DMAENGINE framework assumes that if PQ offload is supported by a
>> DMA device then all 256 PQ coefficients are supported. This assumption
>> does not hold anymore because we now have BCM-SBA-RAID offload engine
>> which supports PQ offload with limited number of PQ coefficients.
>>
>> This patch extends async_tx APIs to handle DMA devices with support
>> for fewer PQ coefficients.
>>
>> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxxxx>
>> Reviewed-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
>
> I don't like this approach. Define an interface for md to query the
> offload engine once at the beginning of time. We should not be adding
> any new extensions to async_tx.

Even if we do capability checks in Linux MD, we still need a way
for DMAENGINE drivers to advertise number of PQ coefficients
handled by the HW.

I agree capability checks should be done once in Linux MD but I don't
see why this has to be part of BCM-SBA-RAID driver patches. We need
separate patchsets to address limitations of async_tx framework.

Regards,
Anup