linux-kernel - Re: [PACTH v2] spi: imx: add 16/32 bits per word support for target mode

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Message-ID: <aP++6ghId1LvQ1NF@lizhi-Precision-Tower-5810>
Date: Mon, 27 Oct 2025 14:50:18 -0400
From: Frank Li <Frank.li@....com>
To: Carlos Song <carlos.song@....com>
Cc: "mkl@...gutronix.de" <mkl@...gutronix.de>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"festevam@...il.com" <festevam@...il.com>,
	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PACTH v2] spi: imx: add 16/32 bits per word support for target
 mode

On Mon, Oct 27, 2025 at 03:39:36AM +0000, Carlos Song wrote:
>
>
> > -----Original Message-----
> > From: Frank Li <frank.li@....com>
> > Sent: Friday, October 24, 2025 9:25 PM
> > To: Carlos Song <carlos.song@....com>
> > Cc: mkl@...gutronix.de; broonie@...nel.org; shawnguo@...nel.org;
> > s.hauer@...gutronix.de; kernel@...gutronix.de; festevam@...il.com;
> > linux-spi@...r.kernel.org; imx@...ts.linux.dev;
> > linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org
> > Subject: Re: [PACTH v2] spi: imx: add 16/32 bits per word support for target
> > mode
> >
> > On Fri, Oct 24, 2025 at 07:31:07PM +0800, carlos.song@....com wrote:
> > > From: Carlos Song <carlos.song@....com>
> > >
> > > Now for ECSPI only support 8 bits per word in target mode.
> > > Enable 16/32 bits per word support for spi-imx target mode.
> > >
> > > Signed-off-by: Carlos Song <carlos.song@....com>
> > > Signed-off-by: Clark Wang <xiaoning.wang@....com>
> > > ---
> > >  drivers/spi/spi-imx.c | 12 ++++++++++--
> > >  1 file changed, 10 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c index
> > > 155ddeb8fcd4..017f83f5dfdf 100644
> > > --- a/drivers/spi/spi-imx.c
> > > +++ b/drivers/spi/spi-imx.c
> > > @@ -424,8 +424,12 @@ static void spi_imx_buf_tx_swap(struct
> > > spi_imx_data *spi_imx)
> > >
> > >  static void mx53_ecspi_rx_target(struct spi_imx_data *spi_imx)  {
> > > -	u32 val = ioread32be(spi_imx->base + MXC_CSPIRXDATA);
> > > +	u32 val = readl(spi_imx->base + MXC_CSPIRXDATA);
> > >
> > > +	if (spi_imx->bits_per_word <= 8)
> > > +		swab32s(&val);
> > > +	else if (spi_imx->bits_per_word <= 16)
> > > +		swahw32s(&val);
> >
> > Needn't swap when bits_per_word > 24, like 32? or our hardware max support
> > to 16?
> >
> > Frank
>
> I think we don't need. We are reading/writing FIFO by 32-bits word. In this case, we just need keep
> the default byte order.
>
> Is it more reasonable only support bits per word=8/16/32 for target mode?
> -b 8/16/32 can cover most use case.

yes, I only can't understand why needn't swap at 32bits workds, but other
needs.

FIFO 31..24  23..16  15..8  7..0
      B0      B1     B2      B3

next you

in memory val is

0x0: B3
0x1: B2
0x2: B1
0x3: B0

swab32s() to  bits_per_work 8

0x0: B0
0x1: B1
0x2: B2
0x3: B3

if bits per_word 16

val

0x0: X
0x1: X
0x2: B1
0x3: B0

after swahw32s change to

0x0: B1
0x1: B0
0x2: x
0x3: x

B0 and B1 still be swapped.

Does SPI defined term word fixed big-endian?

Frank

>
> Carlos
> > >  	if (spi_imx->rx_buf) {
> > >  		int n_bytes = spi_imx->target_burst % sizeof(val);
> > >
> > > @@ -453,12 +457,16 @@ static void mx53_ecspi_tx_target(struct
> > spi_imx_data *spi_imx)
> > >  	if (spi_imx->tx_buf) {
> > >  		memcpy(((u8 *)&val) + sizeof(val) - n_bytes,
> > >  		       spi_imx->tx_buf, n_bytes);
> > > +		if (spi_imx->bits_per_word <= 8)
> > > +			swab32s(&val);
> > > +		else if (spi_imx->bits_per_word <= 16)
> > > +			swahw32s(&val);
> > >  		spi_imx->tx_buf += n_bytes;
> > >  	}
> > >
> > >  	spi_imx->count -= n_bytes;
> > >
> > > -	iowrite32be(val, spi_imx->base + MXC_CSPITXDATA);
> > > +	writel(val, spi_imx->base + MXC_CSPITXDATA);
> > >  }
> > >
> > >  /* MX51 eCSPI */
> > > --
> > > 2.34.1
> > >