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

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Date:   Wed, 8 Feb 2017 14:27:23 +0530
From:   Anup Patel <anup.patel@...adcom.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Vinod Koul <vinod.koul@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Jon Mason <jonmason@...adcom.com>,
        Rob Rice <rob.rice@...adcom.com>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Device Tree <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-crypto@...r.kernel.org,
        linux-raid <linux-raid@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] async_tx: Handle DMA devices having support for
 fewer PQ coefficients

On Tue, Feb 7, 2017 at 11:46 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Tue, Feb 7, 2017 at 1:02 AM, Anup Patel <anup.patel@...adcom.com> wrote:
>> On Tue, Feb 7, 2017 at 1:57 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>>> On Tue, Feb 7, 2017 at 12:16 AM, Anup Patel <anup.patel@...adcom.com> 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@...adcom.com>
>>>> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
>>>
>>> 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