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. -- Ard. -- 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
