On 05/24/2016 08:32 PM, Mark Brown wrote: > On Tue, May 24, 2016 at 08:03:48PM +0200, Christer Weinigel wrote: >> On 05/24/2016 07:20 PM, Mark Brown wrote: > >>> I'm not sure this is something we want to support at all, I >>> can't immediately see anything that does this deliberately in >>> the SPI code and obviously the "bus number" is something of a >>> Linux specific concept which would need some explanation if we >>> were going to document it. It's something I'm struggling a bit >>> to see a robust use case for that isn't better served by >>> parsing sysfs, what's the goal here? > >> If this isn't something that should be in the >> Documentation/devicetree because it's not generig enough, where >> should Linux-specific interpretations such as this be >> documented? > > I'm not clear that we want to document this at all since I am not > clear that there is a sensible use case for doing it. I did ask > for one but you've not articulated one in this reply. I am much > less gung ho than Grant on this one, even as a Linux specific > interface it seems very legacy. It's bloody convenient. I'm working with a Zync board right now where we have multiple SPI ports. Being able to label the ports on the board spi1, spi2 and spi3 and having spidev devices show up as /dev/spidev1.0 instead of dynamic assignment makes things much easier. Especially when doing driver development where unloading and reloading the spi driver module will give it a new dynamic number every time. Yes, it's possible to iterate through all files /sys/class/spi_master and then have a table to map those names to device names and create symlinks to them, it's just painful. It's much easier to do be able to do "cat data >/dev/spidev1.0" from busybox and not have to set up all that infrastructure. And yes, this is on an embedded system using busybox without udev. In addition, right now I have a couple of different variants of the boards that I work on, and with different SPI ports at different addresses. It's rather nice to be able to reuse the same kernel + ramdisk on multiple variants and only have to update the devicetree to get sensible devices names on all variants. /Christer -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
