Re: [PATCH v1 RFC 1/2] spi: introduce fallback to pio

From: Mark Brown <broonie@kernel.org>
To: Robin Gong <yibin.gong@nxp.com>
Cc: "matthias.schiffer@ew.tq-group.com"
	<matthias.schiffer@ew.tq-group.com>,
	"shawnguo@kernel.org" <shawnguo@kernel.org>,
	"s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"robin.murphy@arm.com" <robin.murphy@arm.com>,
	"linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
	Vinod Koul <vkoul@kernel.org>, dl-linux-imx <linux-imx@nxp.com>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	"festevam@gmail.com" <festevam@gmail.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v1 RFC 1/2] spi: introduce fallback to pio
Date: Mon, 15 Jun 2020 13:35:53 +0100	[thread overview]
Message-ID: <20200615123553.GP4447@sirena.org.uk> (raw)
In-Reply-To: <VE1PR04MB6638B43E3AC83286946DABCD899F0@VE1PR04MB6638.eurprd04.prod.outlook.com>

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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: 
> > 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 FIFOs 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 controller
> 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 words,
> 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_one() failue
> in dma and fallback to pio?

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

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