linux-kernel - RE: [PATCH v3 2/3] spi: Add SPI_NO

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Date:   Thu, 3 Dec 2020 08:20:57 +0000
From:   "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     linux-spi <linux-spi@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        "Bogdan, Dragos" <Dragos.Bogdan@...log.com>
Subject: RE: [PATCH v3 2/3] spi: Add SPI_NO_TX/RX support



> -----Original Message-----
> From: Andy Shevchenko <andy.shevchenko@...il.com>
> Sent: Friday, November 27, 2020 4:24 PM
> To: Ardelean, Alexandru <alexandru.Ardelean@...log.com>
> Cc: linux-spi <linux-spi@...r.kernel.org>; devicetree
> <devicetree@...r.kernel.org>; Linux Kernel Mailing List <linux-
> kernel@...r.kernel.org>; Rob Herring <robh+dt@...nel.org>; Mark Brown
> <broonie@...nel.org>; Bogdan, Dragos <Dragos.Bogdan@...log.com>
> Subject: Re: [PATCH v3 2/3] spi: Add SPI_NO_TX/RX support
> 
> On Fri, Nov 27, 2020 at 4:22 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Fri, Nov 27, 2020 at 3:08 PM Alexandru Ardelean
> > <alexandru.ardelean@...log.com> wrote:
> 
> ...
> 
> > > --- a/include/uapi/linux/spi/spi.h
> > > +++ b/include/uapi/linux/spi/spi.h
> > > @@ -43,5 +43,7 @@
> > >  #define        SPI_TX_OCTAL            0x2000          /* transmit with 8 wires */
> > >  #define        SPI_RX_OCTAL            0x4000          /* receive with 8 wires */
> > >  #define        SPI_3WIRE_HIZ           0x8000          /* high impedance turnaround
> */
> > > +#define        SPI_NO_TX               0x10000         /* no transmit wire */
> > > +#define        SPI_NO_RX               0x20000         /* no receive wire */
> >
> > Is it really material for uAPI?
> > Perhaps we may have something like
> > SPI_MODE_USER_MASK in uAPI and
> > in internal headers

Hmm, in a way this could make sense for some SPIDEVs as well, to set these flags and get an error if they try to TX with the NO_TX flag set.
Not really sure about this.
Initially I mechanically added these here as an inertia to the previous patch which is just unifying the headers.

Any other opinions? Thoughts?
Mark?

> >
> > SPI_MODE_KERNEL_MASK with
> > static_assert(_USER_MASK & _KERNEL_MASK); // check conditional
> >
> > ?
> 
> And logically start bits for the kernel from the end (31, 30, ...).
> 
> --
> With Best Regards,
> Andy Shevchenko