Dear Tim, In message <4fb2c002.5030...@am.sony.com> you wrote: > Support same log buffer or tracing buffer in both bootloader and kernel > > ; Summary: Support same log buffer or tracing buffer in both bootloader and > kernel > ; Proposer: Tim Bird - Sony Network Entertainment > > == Description == > It would be nice to share log buffer or trace buffers between the bootloader > and the kernel, > so that either log messages or trace events (respectively) could be coalesced > from both sources in a > unified view.
This has been a standard feature in U-Boot for many years. The corresponding Linux code is also available; see for example https://lkml.org/lkml/2009/1/21/250 and commit 212f61c in git://git.denx.de/linux-denx.git The code has recently been resubmitted by Heiko Schocher, and as far as I can tell it is supposed to hit mainline any time soon. > It appears that U-boot uses a log-buffer format similar to the Linux kernel. Not only similar, but identical (which is intentional). > Note that this is useful for on-box analysis (using 'dmesg' locally, and > getting both > bootloader and kernel messages). It is obvious that someone with a serial > console It actually works round-trip: i. e. you can see in U-Boot the last log messages of the previously running kernel, which may be helpful if messages were written to the log buffer, but the kernel crashed before these could be processed otherwise. And as long as you don't clear the log buffer, you can still read these messages in Linux after rebooting (assuming sane hardware which does not lose memory content during a warmboot - U-Boot takes care to preserve this information during a reboot). > Handling trace events in a coalesced fashion is a whole other issue. ... > * Does u-boot support any tracing code similar to ftrace? No, U-Boot does not support any such feature (yet). > == Scope == > Unknown Scope should be small. As mentioned, the patches are queued. > == Contractor Candidates == > No one so far. I would recommend Heiko Schocher here, who has been working on this in several iterations before, and who submitted the most recent set of patches. Best regards, Wolfgang Denk -- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: w...@denx.de Man is the best computer we can put aboard a spacecraft ... and the only one that can be mass produced with unskilled labor. - Wernher von Braun _______________________________________________ Celinux-dev mailing list Celinux-dev@lists.celinuxforum.org https://lists.celinuxforum.org/mailman/listinfo/celinux-dev
