On 10 June 2015 at 09:30, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > On Tue, Jun 2, 2015 at 12:14 PM, Tomeu Vizoso > <tomeu.vizoso@xxxxxxxxxxxxx> wrote: >> On 2 June 2015 at 10:48, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > >>> 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.) >> >> I understood above that you propose probing devices in order, but now >> you mention that resource getters would block until the dependency is >> fulfilled which confuses me because if we are probing in order then >> all dependencies would be fulfilled before the device in question gets >> probed. > > Sorry, the problem space is a bit convoluted so the answers > get a bit convoluted. Maybe I'm thinking aloud and altering the course > of my thoughts as I type... > > I guess there can be explicit dependencies for resources like this > patch does, but another way would be for all resource fetch functions > to be instrumented, so that you do not block until you try to take > a resource that is not yet there, e.g.: > > regulator_get(...) -> not available, so: > - identify target regulator provider - this will need instrumentation > - probe it > > It then turns out the regulator driver is on the i2c bus, so we > need to probe the i2c driver: > - identify target i2c host for the regulator driver - this will need > instrumentation > - probe the i2c host driver > > i2c host comes out, probes the regulator driver, regulator driver > probes and then the regulator_get() call returns. Hmm, if I understand correctly what you say, this is exactly what this particular series does: regulator_get -> of_platform_device_ensure -> probe() on the platform device that encloses the requested device node (i2c host) -> i2c slave gets probed and the regulator registered -> regulator_get returns the requested resource The downside I'm currently looking at is that an explicit dependency graph would be useful to have for other purposes. For example to print a neat warning when a dependency cannot be fulfilled. Or to refuse to unbind a device which other devices depend on, or to automatically unbind the devices that depend on it, or to print a warning if a device is hotplugged off and other devices depend on it. > This requires instrumentation on anything providing a resource > to another driver like those I mentioned and a lot of overhead > infrastructure, but I think it's the right approach. However I don't > know if I would ever be able to pull that off myself, I know talk > is cheap and I should show the code instead. Yeah, if you can give it a second look and say if it matches what you wrote above, it would be very much appreciated. > Deepest respect for your efforts! Thanks! Tomeu > Yours, > Linus Walleij > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/dri-devel -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
