On Mon, May 25, 2015 at 4:53 PM, Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx> wrote: > have looked into ordered probing as a > better way of solving this than moving nodes around in the DT or playing with > initcall levels. > > While reading the thread [1] that Alexander Holler started with his series to > make probing order deterministic, it occurred to me that it should be possible > to achieve the same by registering devices as they are referenced by other > devices. This is pretty cool, but a too local solution to a global problem. Deferred probe and initcall reordering, silly as they may seem, does not require you to use device tree. The real solution, which I think I pointed out already when we added deferred probe, is to put dependency graphs in the drivers and have the kernel device driver core percolate dependecies by walking the graph on probing driver, removing driver (usually the inverse use case), [runtime] suspend and [runtime] resumeing a driver. Possibly the dependencies will even be different depending on use case. This is what systemd is doing in userspace for starting services: ask for your dependencies and wait for them if they are not there. So drivers ask for resources and wait for them. It also needs to be abstract, so for example we need to be able to hang on regulator_get() until the driver is up and providing that regulator, and as long as everything is in slowpath it should be OK. (And vice versa mutatis mutandis for clk, gpio, pin control, interrupts (!) and DMA channels for example.) So if this should be solved it should be solved in an abstract way in the device driver core available for all, then have calls calling out to DT, ACPI, possibly even PCI or USB (as these enumerate devices themselves) to obtain a certain dependency. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
