On Sat, Sep 05, 2015 at 11:17:59AM +0200, Arnd Bergman wrote: > On Friday 04 September 2015, Lee Jones wrote: > > On Fri, 04 Sep 2015, Arnd Bergmann wrote: > > > > > On Friday 04 September 2015, Lee Jones wrote: > > > > > > If we flip it the other way round, some subsystems derive the firmware > > > > > > name from the 'node name'. For instance, our zeroth General Purpose > > > > > > Co-Processor RemoteProc driver has a corresponding node called > > > > > > 'st231-gp0@40000000'. RemoteProc adds an 'rproc-' prefix and a '-fw' > > > > > > suffix and et voilà, we load file: > > > > > > > > > > > > lib/firmware/rproc-st231-gp0-fw > > > > > > > > > > IMO deriving from the node name seems fragile. Also imposing a linux'ism > > > > > "rproc" prefix on the firmware name doesn't seem correct as the firmwares > > > > > can be shared across OS's. Although this is how remoteproc subsys core > > > > > is currently working. It seems a generic DT firmware binding would actually > > > > > be most useful for the remoteproc subsystem. > > > > > > > > The "rproc-%s-fw", where %s == driver name, is only a fall-back. The > > > > RProc driver is welcome to supply a different firmware name if it > > > > desires. This is where I think a generic 'firmware' property would be > > > > of use. > > > > > > The firmware file name is agreed on between the device driver and the > > > file system, so encoding the linux driver name in it seems appropriate. > > > > > > Generally speaking, I'd say a good policy would be to try basing > > > the firmware name on the "compatible" property strings. That property > > > already contains a hierarchical list of models, which makes it particularly > > > easy to have firmware files for specific models or those that are shared > > > across multiple variations if necessary. Just ask for the most specific > > > compatible string first and try the more specific compatible strings > > > (with an appropriate prefix and/or postfix added by the driver) until > > > a file is found. > > > > It depends what you mean by "basing the firmware name on the > > \"compatible\" property" here. If you mean actually renaming the > > firmware binary file to match a driver's compatible string, that's > > absolutely out of the question. Firmwares are not only OS agnostic, > > but are also independent of any H/W description language a particular > > OS or platform might be using. Using DT'isums to rename these > > binaries is not logical. > > I was thinking of naming the firmware and the compatible string the > same, and often enough that makes sense when both names are picked > by the same person. However, you make a good point that there are cases > where the firmware file already has a name based on some other > decision process and there may be good reasons not to rename the > file. In that case a driver writer can do a lookup table from > one to the other. > The downside of a lookup table of course is that you have to modify > the driver for each new firmware, but then again a lot of drivers > already require that, and others can come up with a policy that lets > you do a programmatic mapping from one to the other by picking > clever compatible strings. You can avoid an in-driver lookup table, though, if you use the compatible string as an "alias" name to the canonical firmware name - implemented with a symlink in userspace. > > However, if you mean simply match on compatible string and supply the > > name from within the driver, that's closer to the mark (as then we can > > at least keep it in-house [kernel]), but it's still not particularly > > practical for the aforementioned reasons mentioned by Peter earlier. > > > > Why not just create a new 'firmware' property? Simples! [0] > > > > [0] http://www.oxforddictionaries.com/definition/english/simples > > My main thought was that loading a different firmware practically > always means that the device behaves in a (sometimes more, sometimes > less) different way, and we want to reflect that with a different > compatible string. Having a 1:1 relation between the two strings > enforces this. I think this is an excellent point. Enforcing that the compatible and firmware travel together is actually a really good idea. As I see it there are two cases where separating them seems like a good idea, but actually isn't: 1) The hardware is identical, and different firmware is used to apply it in different ways. In this case the firmware change is a usage question rather than hardware description and doesn't belong in the device tree. 2) There are several low-level variants on the hardware, which require different firmware images in order to present the same programming interface to the OS. In this case there's a very high chance that some firmware revision will have bugs meaning it's not *quite* compatible with the common programming interface. So, it's correct to present a different compatible property which a driver can use if it needs to work around those bugs. So, I think selecting the firmware based on the compatible property is the correct choice for the DT. Whether the OS uses an in-driver lookup table to go from compatible property to firmware name, or the firmware images are renamed to match the compatible property, or symlinks are used to put the lookup table into the filesystem is an OS design question that shouldn't affect DT binding design. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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