linux-kernel - RE: [PATCH v2 1/4] spi: spi-mem: Add the spi_set_xfer

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Message-ID: <AM0PR04MB4353252D3D6703FA14BCE4BA97EE0@AM0PR04MB4353.eurprd04.prod.outlook.com>
Date:   Sun, 30 Sep 2018 10:48:31 +0000
From:   Chuanhua Han <chuanhua.han@....com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
CC:     "broonie@...nel.org" <broonie@...nel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "eha@...f.com" <eha@...f.com>
Subject: RE: [PATCH v2 1/4] spi: spi-mem: Add the spi_set_xfer_bpw function



> -----Original Message-----
> From: Boris Brezillon <boris.brezillon@...tlin.com>
> Sent: 2018年9月30日 18:40
> To: Chuanhua Han <chuanhua.han@....com>
> Cc: broonie@...nel.org; linux-spi@...r.kernel.org;
> linux-kernel@...r.kernel.org; eha@...f.com
> Subject: Re: [PATCH v2 1/4] spi: spi-mem: Add the spi_set_xfer_bpw function
> 
> On Sun, 30 Sep 2018 10:18:18 +0000
> Chuanhua Han <chuanhua.han@....com> wrote:
> 
> > > -----Original Message-----
> > > From: Boris Brezillon <boris.brezillon@...tlin.com>
> > > Sent: 2018年9月30日 18:04
> > > To: Chuanhua Han <chuanhua.han@....com>
> > > Cc: broonie@...nel.org; linux-spi@...r.kernel.org;
> > > linux-kernel@...r.kernel.org; eha@...f.com
> > > Subject: Re: [PATCH v2 1/4] spi: spi-mem: Add the spi_set_xfer_bpw
> > > function
> > >
> > > Hi Chuanhua,
> > >
> > > On Sun, 30 Sep 2018 17:25:32 +0800
> > > Chuanhua Han <chuanhua.han@....com> wrote:
> > >
> > > > Before we add this spi_transfer to the spi_message chain table, we
> > > > need bits_per_word_mask based on spi_control to set the
> > > > bits_per_word of this spi_transfer.
> > >
> > > Let's make it clearer: this is wrong. The spi-mem protocol is just
> > > using bytes, not custom size words. Fix the fsl-dspi driver if
> > > needed, but don't try to adjust
> > > xfer->bits_per_word in spi-mem.c, because this is inappropriate.
> > The value of bits_per_word is only known before the
> > spi_message_add_tail function is called,
> 
> No, it's not. It's known from the beginning, and spi_setup() defaults to 8 when
> spidev->bits_per_word is 0, which is exactly what we want. Then, when you
> send a message through, spi_sync(), spi_validate() makes sure that each
> transfer in the message has a
> xfer->bits_per_word != 0 and when that's not the case, it sets it to
> spi->bits_per_word [2].
> 
> Really, there's nothing to fix in spi-mem.c, because it's already doing the right
> thing (leaving ->bits_per_word to 0 so that it's set to
> spi->bits_per_word, which should be 8). Maybe we have a bug somewhere
> else though.
> 
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> [2]https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Feli
> xir.bootlin.com%2Flinux%2Fv4.19-rc5%2Fsource%2Fdrivers%2Fspi%2Fspi.c%23
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I'll take the time to study this.
October 1 to October 7 is the National Day of our country. I need to take a vacation.
I may not reply to the email in time during this period. 
Thank you very much for your valuable advice!!!