Re: [PATCH] spi: Force the registration of the spidev devices

Geert Uytterhoeven
2015-05-13T19:10:52Z

On Wed, May 13, 2015 at 2:51 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
>> > This also adds an i2cdev-like feeling, where you get all the
>> > spidev devices all the time, without any modification.
>>
>> I2C is a bit safer here since it's a shared bus so you can't do
>> anything to devices not connected to the bus by mistake.
>
> I'm not sure to understand what you mean here. How is SPI different
> from that aspect?

If you talk to a nonexistent i2c device, nothing happens, as it just sends
a message with a nonexistent address on the shared bus.

If you talk to a nonexistent spi device, hell may break loose if e.g. some
"smart" hardware engineer used the "unused" CS as a pull-up for the
_RESET line on an external device... It's a bit like banging random
"unused" GPIOs.

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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