On 02/06/2020 00:12, Rob Herring wrote: Hi, > On Mon, Jun 1, 2020 at 4:15 AM André Przywara <andre.przywara@xxxxxxx> wrote: >> >> On 28/05/2020 14:30, André Przywara wrote: >> >> Hi, >> >>> On 28/05/2020 03:48, Guenter Roeck wrote: >>> >>> Hi Guenter, >>> >>>> On Wed, May 13, 2020 at 11:30:00AM +0100, Andre Przywara wrote: >>>>> The devicetree compiler complains when DT nodes without a reg property >>>>> live inside a (simple) bus node: >>>>> Warning (simple_bus_reg): Node /bus@8000000/motherboard-bus/refclk32khz >>>>> missing or empty reg/ranges property >>>>> >>>>> Move the fixed clocks, the fixed regulator, the leds and the config bus >>>>> subtree to the root node, since they do not depend on any busses. >>>>> >>>>> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx> >>>> >>>> This patch results in tracebacks when booting the vexpress-a15 machine >>>> with vexpress-v2p-ca15-tc1 devicetree file in qemu. Reverting it as well >>>> as the subsequent patches affecting the same file (to avoid revert >>>> conflicts) fixes the problem. >>> >>> Many thanks for the heads up! I was able to reproduce it here. On the >>> first glance it looks like the UART is probed before the clocks now, >>> because the traversal of the changed DT leads to a different probe >>> order. I will look into how to fix this. >> >> Turned out to be a bit more complicated: >> The arm,vexpress,config-bus driver walks up the device tree to find a >> arm,vexpress,site property [1]. With this patch the first parent node >> with that property it finds is now the root node, with the wrong site ID >> (0xf instead of 0x0). So it queries the wrong clocks (those IDs are >> actually reserved there), and QEMU reports back "0", consequently [2]. >> Finding a clock frequency in the range of [0, 0] won't get very far. >> >> Possible solutions are: >> 1) Just keep the mcc and its children at where it is in mainline right >> now, so *partly* reverting this patch. This has the problem of still >> producing a dtc warning, so kind of defeats the purpose of this patch. >> >> 2) Add a "arm,vexpress,site = <0>;" line to the "mcc" node itself. >> Works, but looks somewhat dodgy, as the mcc node should really be a >> child of the motherboard node, and we should not hack around this. >> >> 3) Dig deeper and fix the DT in a way that makes dtc happy. Might >> involve (dummy?) ranges or reg properties. My gut feeling is that >> arm,vexpress-sysreg,func should really have been "reg" in the first >> place, but that's too late to change now, anyway. >> >> I will post 2) as a fix if 3) turns out to be not feasible. > > I would just do 1). > > To some extent, the warnings are for avoiding poor design on new > bindings. We need a way to distinguish between existing boards and new > ones. Maybe dts needs to learn some warning disable annotations or we > need per target warning settings (DTC_FLAGS_foo.dtb ?). Or maybe this > check is just too strict. So I was always wondering about this check, actually. A simple-bus describes a bus which is mapped into the CPU address space (in contrast to say an I2C bus, for instance). So children of this bus node typically have a reg property. Now also those simple-bus nodes seem to be used to logically group hardware in a DT (see this "motherboard" node here). *If* we go with this, we should also allow other subnodes, for instance fixed-clocks: after all there is probably an actual fixed crystal oscillator on the motherboard, so it would also belong in there. I see that (ab)using simple-bus for *just* grouping nodes is probably not a good design, but I don't see why *every* child must be mapped into the address space. Maybe dtc's simple-bus check should indeed be relaxed, to just require *at least one* child with a reg or ranges property, but also allow other nodes? Cheers, Andre
