linux-kernel - Re: [PATCH v2 2/4] spi: spi-fsl-dspi: Fix delete the processing of undefined bitmask for rxdata

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Message-ID: <20180930121707.4724edd6@bbrezillon>
Date:   Sun, 30 Sep 2018 12:17:07 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Chuanhua Han <chuanhua.han@....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 2/4] spi: spi-fsl-dspi: Fix delete the processing of
 undefined bitmask for rxdata

On Sun, 30 Sep 2018 10:10:14 +0000
Chuanhua Han <chuanhua.han@....com> wrote:

> > -----Original Message-----
> > From: Boris Brezillon <boris.brezillon@...tlin.com>
> > Sent: 2018年9月30日 18:07
> > 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 2/4] spi: spi-fsl-dspi: Fix delete the processing of
> > undefined bitmask for rxdata
> > 
> > On Sun, 30 Sep 2018 17:25:33 +0800
> > Chuanhua Han <chuanhua.han@....com> wrote:
> >   
> > > This patch fixes the problem of rxdata being equal to 0 during the
> > > XSPI mode transfer of the dspi controller.
> > > In XSPI mode, If it is not deleted, the value of rxdata will be equal
> > > to 0, and the data received will not be received correctly, causing
> > > the receiving transfer of the spi to fail.
> > >
> > > Signed-off-by: Chuanhua Han <chuanhua.han@....com>
> > > ---
> > > Changes in v2:
> > >  -The original patch is divided into multiple patches(the original
> > > patch theme is "spi: spi-fsl-dspi: Fix support for XSPI transport
> > > mode"),one of which is segmented.
> > >
> > >  drivers/spi/spi-fsl-dspi.c | 3 ---
> > >  1 file changed, 3 deletions(-)
> > >
> > > diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
> > > index 3082e72e4f6c..4dc1064bf408 100644
> > > --- a/drivers/spi/spi-fsl-dspi.c
> > > +++ b/drivers/spi/spi-fsl-dspi.c
> > > @@ -243,9 +243,6 @@ static void dspi_push_rx(struct fsl_dspi *dspi, u32  
> > rxdata)  
> > >  	if (!dspi->rx)
> > >  		return;
> > >
> > > -	/* Mask of undefined bits */
> > > -	rxdata &= (1 << dspi->bits_per_word) - 1;
> > > -  
> > 
> > Why not  
> In xspi mode, the value of rxdata after the statement is processed is equal to 0 no matter what data is received.

Only if dspi->bits_per_word is 0.

Actually, I just had a look, and xfer->bits_per_word should never be 0
because spi_validate() makes sure it's initialized [1]. Don't know
where dpsi->bits_per_word comes from, but maybe you have a problem
there (dpsi->bits_per_word and xfer->bits_per_word not in sync).

[1]https://elixir.bootlin.com/linux/v4.19-rc5/source/drivers/spi/spi.c#L2869