Re: spidev instantiated from DT

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Giuseppe,

On Sun, Dec 11, 2016 at 1:03 PM, Giuseppe Lippolis
<giu.lippolis@xxxxxxxxx> wrote:
> in the spidev.c driver there is a check preventing to export the SPI
> subsystem to the userspace.
> The commit message state:
>
>         spi: spidev: Warn loudly if instantiated from DT as "spidev"
>
>     Since spidev is a detail of how Linux controls a device rather than a
>     description of the hardware in the system we should never have a node
>     described as "spidev" in DT, any SPI device could be a spidev so this
>     is just not a useful description.
>
>     In order to help prevent users from writing such device trees generate a
>     warning if spidev is instantiated as a DT node without an ID in the
> match
>     table.
>
>     Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
>
> Currently in the spidec.c are registered two devices to use "legally" this
> driver:
>     { .compatible = "rohm,dh2228fv" },
>     { .compatible = "lineartechnology,ltc2488" },
>
> I cannot fully understand the rationale.
> I have a board mounting an spi device. Currently no dedicated driver for
> this devices exists.

But you can still describe the SPI device in DT, right?
Then you can add its compatible value to spidev.c now, until a dedicated
driver becomes available.

> So in my opinion, now, make sense to describe a device-tree with a "generic"
> driver, allowing the userspace to control the device. When at the end a
> dedicated driver will be available an update of the device tree will be
> possible.

Hmm... So you would change DT, which describes the hardware, while the actual
hardware hasn't changed?

Does that help to understand the rationale?

> In alternative, make sense to add a dedicated .compatible = "xxx,yyy"
> statements to attach the spidev driver to the specific device and allowing
> the DT description as soon as a dedicated driver will be not available?

Please add the dedicated compatible statement to spidev.c.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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