On 11/4/2015 10:51 AM, Ard Biesheuvel wrote: > On 4 November 2015 at 19:49, Christopher Covington <cov@xxxxxxxxxxxxxx> wrote: >> On 11/04/2015 08:31 AM, Christoffer Dall wrote: >>> On Tue, Nov 03, 2015 at 01:39:44PM -0600, Rob Herring wrote: >>>> On Tue, Nov 3, 2015 at 1:17 PM, Mario Smarduch <m.smarduch@xxxxxxxxxxx> wrote: >>>>> On 11/3/2015 9:55 AM, Will Deacon wrote: >>>>>> On Tue, Nov 03, 2015 at 09:44:52AM -0800, Mario Smarduch wrote: >>>>>>> On 11/3/2015 8:33 AM, Christopher Covington wrote: >>>>>>>> On 11/02/2015 06:51 PM, Mario Smarduch wrote: >>>>>>>>> this is a re-post from couple weeks ago, please take time to review this >>>>>>>>> simple patch which simplifies DEBUG_LL and prevents kernel crash on virtual >>>>>>>>> platforms. >>>>>>>>> >>>>>>>>> Before this patch DEBUG_LL for 'dummy virtual machine': >>>>>>>>> >>>>>>>>> ( ) Kernel low-level debugging via EmbeddedICE DCC channel >>>>>>>>> ( ) Kernel low-level debug output via semihosting I/O >>>>>>>>> ( ) Kernel low-level debugging via 8250 UART >>>>>>>>> ( ) Kernel low-level debugging via ARM Ltd PL01x Primecell >>>>>>>>> >>>>>>>>> In summary if debug uart is not emulated kernel crashes. >>>>>>>>> And once you pass that hurdle, uart physical/virtual addresses are unknown. >>>>>>>>> DEBUG_LL comes in handy on many occasions and should be somewhat >>>>>>>>> intuitive to use like it is for physical platforms. For virtual platforms >>>>>>>>> user may start daubting the host and get into a bigger mess. >>>>>>>>> >>>>>>>>> After this patch is applied user gets: >>>>>>>>> >>>>>>>>> (X) Kernel low-level debugging on QEMU Virtual Platform >>>>>>>>> ( ) Kernel low-level debugging on Kvmtool Virtual Platform >>>>>>>>> ..... above repeated .... >>>>>>>>> >>>>>>>>> The virtual addresses selected follow arm reference models, high in vmalloc >>>>>>>>> section with high mem enabled and guest running with >= 1GB of memory. The >>>>>>>>> offset is leftover from arm reference models. >>>>>>>> >>>>>>>> Which model? It doesn't appear to match the vexpress AEM/RTSM/FVP/whatever >>>>>>>> which used 0x1c090000 for UART0. >>>>>>> >>>>>>> I recall QEMU virt model had it's own physical address map, for sure I saw the >>>>>>> virtio-mmio regions assigned in some ARM document. Peter would you know? >>>>>>> >>>>>>> As far as kvmtool I'm not sure, currently PC1 COM1 port is used? Andre will that >>>>>>> stay fixed? >>>>>> >>>>>> We make absolutely no guarantees about the memory map provided by kvmtool. >>>>> >>>>> If that's also the case for qemu, then I guess the best you can do is find a way >>>>> to dump the device tree. Find the uart, physical address and try figure out the >>>>> virtual address. >>>>> >>>>> Pretty involved, hoped for something more automated since that's a handy feature. >>>> >>>> You really only need LL_DEBUG now if you are debugging very early code >>>> before memory is setup and/or bad memory. Use earlycon instead which >>>> should already be supported both via the pl011 or semihosting. I used >>>> it with QEMU semihosting support. >>>> >>> Then we should really document how to use that with qemu's virt platform >>> and kvmtool's platform on both 32-bit and 64-bit so that users can >>> easily figure out what they're doing wrong when they get no output. >>> >>> In practice, the address for the pl011 is quite unlikely to change, I >>> dare speculate, so that documentation shouldn't need frequent updating. >> >> Is it not on by default since the following change? >> >> http://git.qemu.org/?p=qemu.git;a=commitdiff;h=f022b8e95379b0433d13509706b66f38fc15dde8 >> > > Yes, but it still requires the plain 'earlycon' argument (i.e, without > '=pl011,...') to be passed on the kernel command line if you want > early output. > I spent time debugging 'earlycon' for pl011, ironically using DEBUG_LL, from the looks of it no mmio uart should work for armv7. It appears earlycon_map() requires a fixed mapping similar to arm64. Comparing both options, DEBUG_LL takes you from kernel decompress code to early FDT parsing. A lot of early_print() calls won't work if DEBUG_LL is not enabled including dump_machine_table which ends in a endless loop. IMO it's worth turning this option on for that and other reasons. 'earlycon' is enabled some ways up in setup_arch(). As far as the patch, providing a hint to the user with probable uart addresses would help and in the worst case "see the latest device tree for the virtual platform". - Mario -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
