Messages in this thread | | | Subject | Re: [linux-sunxi] [PATCH 2/3] spidev: Add DT binding example. | From | Martin Sperl <> | Date | Mon, 27 Apr 2015 18:25:26 +0200 |
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> On 27.04.2015, at 17:27, Mark Brown <broonie@kernel.org> wrote: > > > OK, so that is just a default overlay which is abusing the fact that we > will bind to spidev without a DT compatible and when the binding is > undocumented (which also applies to other devices and buses sadly). > > Unfortunately nobody ever mentioned this upstream and the feedback > upstream that listing spidev in a DT is a bad idea has been ignored.
Maybe it should also have been documented as such in Documentation/spi/spidev or in Documentation/devicetree/bindings/spi/
> The whole reason we're doing this in the first place is that we got sick > of telling people that using spidev in DTs like this was a bad idea.
The only reference I found in my history of the spi-list is this email: > On 08.10.2014, at 22:05, Mark Brown <broonie@kernel.org> wrote: > > On Wed, Oct 08, 2014 at 02:27:08PM -0500, tthayer@opensource.altera.com wrote: > >> + spidev@0 { >> + compatible = "spidev"; >> + reg = <0>; /* chip select */ >> + spi-max-frequency = <100000000>; >> + }; > > No, if you're putting spidev into the DT that's broken - describe the > hardware, not the software you're using to control it.
And google found this patch from a little earlier: http://comments.gmane.org/gmane.linux.ports.arm.kernel/231050
So finding this piece of information on the “use-policy” is quite hard - google finds lots of links where it is described as working that way.
> It does sound like the people maintianing the u-boot fork for the Pi > need to talk to both u-boot upstream (nothing here is specific to the > Pi that I can see) and the kernel community a bit more. I'd be a bit > worried that they may be relying on other things that just happen to > work without being intentional (and are therefore more vulnerable to > issues) and it's a bit depressing to see things like this stuck in a > fork where only a limited community can make use of them. Actually this functionality is not in u-boot, but in the firmware boot-loader itself, which can load the kernel (and the devicetree) without u-boot, but which can also load u-boot as an additional intermediate boot-stage.
>> The only thing that could possibly be better would be that >> the user would define the "real" name of the device in the >> device tree and spidev would bind to it if there is no driver >> available (but that would require this "fallback" binding by >> spidev in case of no driver). > > Yes, that is exactly the solution I'd suggest - change the UI to provide > a DT compatible to be used for the new device. That would also have the > benefit of meaning that users who have connected some device that does > have a driver that works with a simple binding wouldn't need to write an > overlay which seems like it should be useful.
Well then why did you just make the system complain loudly and bringing problems to people instead of solving it in a usable manner that does not require people to maintain an out of tree patch to work around that warning?
We still have the one-line warning about using the depreciated spi_master.transfer interface, but it is not such loud warning as this one.
I guess the time spent discussing this could have been better spent implementing that solution instead.
All we need is a volunteer to get that implemented.
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