Re: [PATCH] spi: spidev: Warn loudly if instantiated from DT as "spidev"

[Martin Sperl <kernel@xxxxxxxxxxxxxxxx>]

> On 28.03.2015, at 00:42, Mark Brown <broonie@xxxxxxxxxx> wrote:
> 
> 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>

So what is now the “correct way” to create a spidev device via the
device-tree? 

There is no update in Documentation/spi/spidev how to achieve this in
a “correct” manner besides using board_info and the mentioned possible
sysfs approach, which is not implemented as an alternative.

If I still put spidev into the device-tree - as there is not other way
to do it as far as I known - then it produces an issue:
[  328.255338] spidev spi32765.1: buggy DT: spidev listed directly in DT
[  328.255399] ------------[ cut here ]------------
[  328.255443] WARNING: CPU: 0 PID: 2968 at drivers/spi/spidev.c:730 spidev_probe+0x198/0x1e4 [spidev]()
[  328.255457] Modules linked in: spidev(+) spi_bcm2835 bcm2835_wdt bcm2835_dma virt_dma
... lots more lines with stack-trace ...

So it is just a warning triggered by:
                 WARN_ON(spi->dev.of_node &&
                         !of_match_device(spidev_dt_ids, &spi->dev));

But still it is “irritating” as, it produces lots of messages in dmesg.

Note that on a raspberry pi the 2 SPI devices are by default configured 
as spidev and only overlays would change the settings to a different
alias. So this change will impact that default immediately.

Thus I wonder if it is wise to produce potential “support issues" for 
distributions triggered by this patch.

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