Hi Grant, On May 27, 2014, at 3:12 PM, Grant Likely wrote: > On Mon, 26 May 2014 16:42:44 -0700, Guenter Roeck <linux@xxxxxxxxxxxx> wrote: >> On 05/26/2014 03:36 PM, Sebastian Reichel wrote: >>> Hi, >>> >>> On Mon, May 26, 2014 at 10:33:03PM +0100, Grant Likely wrote: >>>> After thinking about it more, I think it is very likely that removing >>>> all the overlays is the correct thing to do in the kexec use-case. When >>>> kexec-ing, it makes sense that we'd want the exact same behaviour from >>>> the kexec'ed kernel. That means we want the device drivers to do the >>>> same thing including loading whatever overlays they depend on. >>>> >>>> If the flattened tree was left applied, then the behaviour becomes >>>> different. >>>> >>>> I say always remove the overlays unless explicitly told not to, but I'm >>>> struggling to come up with use cases where keeping them applied is >>>> desirable. >>> >>> I would assume, that I want them applied in most cases. DT describes >>> the hardware. If I kexec into a new kernel I change software, not >>> hardware. >>> >>> Maybe I'm missing the main purpose of the feature. I currently see >>> two useful usecases for DT overlays: >>> >>> 1. The dtb the kernel is booted with cannot be changed for some >>> reason, but the board has additional hardware attached (e.g. >>> the user added a sensor on the i2c bus) >>> 2. The hardware is changed on the fly (e.g. the user flashed the >>> FPGA part of a zynq processor), sensors on i2c bus, ... >>> >>> In both cases the kernel should be booted with the additional >>> overlay information IMHO. Though for the second case it should >>> be possible to remove the "programmed" hardware information >>> somehow. >>> >> >> 3. Some hot-plug device or card is inserted or removed. >> >> I would argue that the kernel should _not_ be booted with the overlay in place. >> Otherwise the code handling overlays would have to have special handling >> for the restart case, which is much more complex than just to re-insert >> the overlay when it is determined that the device or card is still there. > > Exactly. > Looks like we are levitating to the 'remove overlays on kexec' approach. Is that correct? > g. > Regards -- Pantelis -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
