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

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Message-ID: <CAHp75Vcd4t=RqC31S-b1PXMtd=8sypSLhTrSgRD9hbpSqOphoQ@mail.gmail.com>
Date:   Fri, 27 Nov 2020 16:22:51 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Alexandru Ardelean <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 3:08 PM Alexandru Ardelean
<alexandru.ardelean@...log.com> wrote:
> Transmit/receive only is a valid SPI mode. For example, the MOSI/TX line
> might be missing from an ADC while for a DAC the MISO/RX line may be
> optional. This patch adds these two new modes: SPI_NO_TX and
> SPI_NO_RX. This way, the drivers will be able to identify if any of
> these two lines is missing and to adjust the transfers accordingly.

...

> +       /*
> +        * check mode to prevent that any two of DUAL, QUAD and NO_MOSI/MISO
> +        * are set at the same time
>          */

Since you are here,
 check -> Check
 time -> time.

...

> +       if ((hweight_long(spi->mode &
> +               (SPI_TX_DUAL | SPI_TX_QUAD | SPI_NO_TX)) > 1) ||
> +           (hweight_long(spi->mode &
> +               (SPI_RX_DUAL | SPI_RX_QUAD | SPI_NO_RX)) > 1)) {
>                 dev_err(&spi->dev,
> -               "setup: can not select dual and quad at the same time\n");
> +               "setup: can not select any two of dual, quad and no-rx/tx "
> +               "at the same time\n");

Don't split literals, and probably rephrase (If I can't set 2, can I set 3?)
   "setup: can't select more than one out of dual, quad, and no-Rx /
no-Tx at the same time\n");

> --- 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

SPI_MODE_KERNEL_MASK with
static_assert(_USER_MASK & _KERNEL_MASK); // check conditional

?

-- 
With Best Regards,
Andy Shevchenko