Re: [PATCH 02/13] spi: spi-fsl-lpspi: Set correct chip-select polarity bit

[Frank Li <Frank.li@nxp.com>]

On Mon, Aug 18, 2025 at 02:05:16PM +0100, James Clark wrote:
>
>
> On 14/08/2025 5:49 pm, Frank Li wrote:
> > On Thu, Aug 14, 2025 at 05:06:42PM +0100, James Clark wrote:
> > > From: Larisa Grigore <larisa.grigore@nxp.com>
> > >
> > > The driver currently supports multiple chip-selects, but only sets the
> > > polarity for the first one (CS 0). Fix it by setting the PCSPOL bit for
> > > the desired chip-select.
> > >
> > > Fixes: 5314987de5e5 ("spi: imx: add lpspi bus driver")
> > > Signed-off-by: Larisa Grigore <larisa.grigore@nxp.com>
> > > Signed-off-by: James Clark <james.clark@linaro.org>
> > > ---
> > >   drivers/spi/spi-fsl-lpspi.c | 6 ++++--
> > >   1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/spi/spi-fsl-lpspi.c b/drivers/spi/spi-fsl-lpspi.c
> > > index d44a23f7d6c1..c65eb6d31ee7 100644
> > > --- a/drivers/spi/spi-fsl-lpspi.c
> > > +++ b/drivers/spi/spi-fsl-lpspi.c
> > > @@ -70,7 +70,7 @@
> > >   #define DER_TDDE	BIT(0)
> > >   #define CFGR1_PCSCFG	BIT(27)
> > >   #define CFGR1_PINCFG	(BIT(24)|BIT(25))
> > > -#define CFGR1_PCSPOL	BIT(8)
> > > +#define CFGR1_PCSPOL_MASK	GENMASK(11, 8)
> > >   #define CFGR1_NOSTALL	BIT(3)
> > >   #define CFGR1_HOST	BIT(0)
> > >   #define FSR_TXCOUNT	(0xFF)
> > > @@ -425,7 +425,9 @@ static int fsl_lpspi_config(struct fsl_lpspi_data *fsl_lpspi)
> > >   	else
> > >   		temp = CFGR1_PINCFG;
> > >   	if (fsl_lpspi->config.mode & SPI_CS_HIGH)
> > > -		temp |= CFGR1_PCSPOL;
> > > +		temp |= FIELD_PREP(CFGR1_PCSPOL_MASK,
> > > +				   BIT(fsl_lpspi->config.chip_select));
> > > +
> >
> > Feel like FILED_PREP(..., BIT()) is stranged.
> >
> > I suggest #define CFGR1_PCSPOL(x) BIT((x) + 8)
> >
> > Frank
>
> It's using an existing macro that everyone knows though and I found 65
> instances of exactly this. It can be read as "set bit X and put it into the
> PCSPOL field without any further investigation.

Where have such pattern in kernel?

Frank

>
> If we make a new macro, first the reader will have to jump to it, then it
> still doesn't immediately explain what the "+ 8" part is. Using FIELD_PREP()
> also has the potential to use autogenerated field masks from a machine
> readable version of the reference manual. You can't statically check your
> macro to see if + 8 is correct or not, and it also doesn't catch overflow
> errors like FIELD_PREP() does.
>
> There might be an argument to add a new global macro like FIELD_BIT(mask,
> bit). But it's not very flexible (can't set multiple bits) and you can
> already accomplish the same thing by adding BIT() to the existing one.
>
> Thanks
> James
>
> >
> > >   	writel(temp, fsl_lpspi->base + IMX7ULP_CFGR1);
> > >
> > >   	temp = readl(fsl_lpspi->base + IMX7ULP_CR);
> > >
> > > --
> > > 2.34.1
> > >
>