linux-kernel - Re: [PATCH v3 3/4] dmaengine: Add Broadcom SBA RAID driver

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Date:   Tue, 14 Feb 2017 09:30:04 +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 v3 3/4] dmaengine: Add Broadcom SBA RAID driver

On Mon, Feb 13, 2017 at 2:43 PM, Anup Patel <anup.patel@...adcom.com> wrote:
> On Fri, Feb 10, 2017 at 11:20 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>> On Fri, Feb 10, 2017 at 1:07 AM, Anup Patel <anup.patel@...adcom.com> wrote:
>>> The Broadcom stream buffer accelerator (SBA) provides offloading
>>> capabilities for RAID operations. This SBA offload engine is
>>> accessible via Broadcom SoC specific ring manager.
>>>
>>> This patch adds Broadcom SBA RAID driver which provides one
>>> DMA device with RAID capabilities using one or more Broadcom
>>> SoC specific ring manager channels. The SBA RAID driver in its
>>> current shape implements memcpy, xor, and pq operations.
>>>
>>> Signed-off-by: Anup Patel <anup.patel@...adcom.com>
>>> Reviewed-by: Ray Jui <ray.jui@...adcom.com>
>>> ---
>>>  drivers/dma/Kconfig        |   13 +
>>>  drivers/dma/Makefile       |    1 +
>>>  drivers/dma/bcm-sba-raid.c | 1711 ++++++++++++++++++++++++++++++++++++++++++++
>>>  3 files changed, 1725 insertions(+)
>>>  create mode 100644 drivers/dma/bcm-sba-raid.c
>>>
>>> diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
>>> index 263495d..bf8fb84 100644
>>> --- a/drivers/dma/Kconfig
>>> +++ b/drivers/dma/Kconfig
>>> @@ -99,6 +99,19 @@ config AXI_DMAC
>>>           controller is often used in Analog Device's reference designs for FPGA
>>>           platforms.
>>>
>>> +config BCM_SBA_RAID
>>> +       tristate "Broadcom SBA RAID engine support"
>>> +       depends on (ARM64 && MAILBOX && RAID6_PQ) || COMPILE_TEST
>>> +       select DMA_ENGINE
>>> +       select DMA_ENGINE_RAID
>>> +       select ASYNC_TX_ENABLE_CHANNEL_SWITCH
>>
>> ASYNC_TX_ENABLE_CHANNEL_SWITCH violates the DMA mapping API and
>> Russell has warned it's especially problematic on ARM [1].  If you
>> need channel switching for this offload engine to be useful then you
>> need to move DMA mapping and channel switching responsibilities to MD
>> itself.
>>
>> [1]: http://lists.infradead.org/pipermail/linux-arm-kernel/2011-January/036753.html
>
> Actually driver works fine with/without
> ASYNC_TX_ENABLE_CHANNEL_SWITCH enabled
> so I am fine with removing dependency on this config option.

I stand corrected.

Previously, when I had tried removing
ASYNC_TX_ENABLE_CHANNEL_SWITCH
from BCM_SBA_RAID config option it worked because other
drivers such xgene-dma and mv_xor_v2 are selecting this option.

The BCM-SBA-RAID driver requires
ASYNC_TX_ENABLE_CHANNEL_SWITCH option

There is no issue reported for
ASYNC_TX_ENABLE_CHANNEL_SWITCH
with ARM64 kernel.

The issue you pointed out was with ARM kernel.

We will have to select
ASYNC_TX_ENABLE_CHANNEL_SWITCH
for BCM-SBA-RAID driver
just like other ARM64 RAID drivers such
as xgene-dma and mv_xor_v2.
(Refer, XGENE_DMA and MV_XOR_V2 options)

Regards,
Anup