linux-kernel - RE: [PATCH v1 RFC 1/2] spi: introduce fallback to pio

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Message-ID: <VE1PR04MB6638C65257F41072C3D61583899C0@VE1PR04MB6638.eurprd04.prod.outlook.com>
Date:   Mon, 15 Jun 2020 13:35:01 +0000
From:   Robin Gong <yibin.gong@....com>
To:     Mark Brown <broonie@...nel.org>
CC:     Vinod Koul <vkoul@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "matthias.schiffer@...tq-group.com" 
        <matthias.schiffer@...tq-group.com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>,
        "linux-spi@...r.kernel.org" <linux-spi@...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>
Subject: RE: [PATCH v1 RFC 1/2] spi: introduce fallback to pio

On 2020/06/15 20:36 Mark Brown <broonie@...nel.org> wrote: 
> On Sun, Jun 14, 2020 at 01:04:57PM +0000, Robin Gong 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.
Okay, thanks Mark.
> 
> > > 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.
Then how about choosing specific error code for such dma not ready case where
nothing went out on the bus neither? 

> 
> > 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.