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

[Anup Patel]

On Tue, Feb 7, 2017 at 11:46 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> On Tue, Feb 7, 2017 at 1:02 AM, Anup Patel <anup.patel@xxxxxxxxxxxx> wrote:
>> 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.
>
> Right, separate enabling before we pile on new hardware support to a
> known broken framework.

Linux Async Tx not broken framework. The issue is:
1. Its not complete enough
2. Its not optimized for very high through-put offload engines

Regards,
Anup