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Date:   Mon, 15 Jun 2020 13:35:53 +0100
From:   Mark Brown <broonie@kernel.org>
To:     Robin Gong <yibin.gong@nxp.com>
Cc:     Vinod Koul <vkoul@kernel.org>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
        "s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
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        "robin.murphy@arm.com" <robin.murphy@arm.com>,
        "matthias.schiffer@ew.tq-group.com" 
        <matthias.schiffer@ew.tq-group.com>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        dl-linux-imx <linux-imx@nxp.com>,
        "linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 RFC 1/2] spi: introduce fallback to pio
Message-ID: <20200615123553.GP4447@sirena.org.uk>
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On Sun, Jun 14, 2020 at 01:04:57PM +0000, Robin Gong wrote:
> On 2020/06/12 22:16 Mark Brown <broonie@kernel.org> wrote:=20
> > On Fri, Jun 12, 2020 at 01:48:41PM +0000, Robin Gong wrote:
> > > On 2020/06/12 18:14 Mark Brown <broonie@kernel.org> wrote:

Please delete unneeded context from mails when replying.  Doing this
makes it much easier to find your reply in the message, helping ensure
it won't be missed by people scrolling through the irrelevant quoted
material.

> > No, I mean that the reason the DMA transfer fails may be something that
> > happens after we've started putting things on the bus - the bit about F=
IFOs is
> > just a random example of an error that could happen.

> Sorry Mark for that I can't get your point... The bus error such as data =
corrupt
> seems not the spi core's business since it can only be caught in spi cont=
roller
> driver or upper level such as mtd driver (spi-nor) which know what's the =
failure
> happen at spi bus HW level or what's the correct data/message. In other w=
ords,
> spi core can't detect such error by transfer_one().

If we see an error in transfer_one() it could be from anything, we've no
idea what happened on the bus - the controller may have got part way
through the transfer before failing.

> But despite of that case, do you think this patch is valid for transfer_o=
ne() failue
> in dma and fallback to pio?

No, not unless we know that nothing went out on the bus.

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