[linux-pm] sleepy linux self-test
david-b at pacbell.net
Sat Feb 2 11:47:44 PST 2008
On Saturday 02 February 2008, Ingo Molnar wrote:
> * David Brownell <david-b at pacbell.net> wrote:
> > On Saturday 02 February 2008, Ingo Molnar wrote:
> > >
> > > i'd really love to have a /dev/rtc device compatibility APIs, both
> > > inside and outside the kernel.
> > Unfortunately the /dev/rtc code became a legacy API for good reasons.
> > Like not recognizing that all the world's not a PC, with a single RTC
> > that clones a long-obsolete chip from Motorola ... and not having been
> > specified in a hardware-neutral manner. Oh, and of course not all
> > systems actually used the same RTC driver anyway; it's not like there
> > was just *one* such programming interface to worry about.
> i dont get it - please give me specific technological reasons
In a word: -ENOPATCH. ;)
> why on my
> PC /dev/rtc couldnt be mapped to /dev/rtc0 - without requiring any
> user-space changes. The APIs seem mostly covered, or at least mappable.
> Why should the transition to a new driver require user-level changes?
> (beyond the obvious extensions, but those should show up as extensions.)
So far as I'm aware, the only issue visible to userspace relate to
the legacy driver's use of "/dev/rtc" not "/dev/rtc0" ... which has
previously been "solved" by symlinking "rtc" -> "rtc0", possibly with
assistance from udev. (Related: the major/minor number of /dev/rtc.)
Is that your understanding too?
The "why" is that nobody has been sufficiently bothered by the need
to symlink that they produced a kernel patch to compensate.
> In fact i detest the old RTC code with a vengence, so dont understand
> this as some invitation to flame or something - i simply want YOUR new
> code to be utilized more!
Good to know! :)
But so you're clear ... not "my" code, mostly. Alessandro Zummo started
this framework, based in part on Russell King's framework for RTCs that
were integrated into ARM based SOCs. I contributed a bunch, including
rtc-cmos to let the PC side of Linux join the effort.
> I just dont see the specific technological
> reasons of why there is no .config switch to switch the legacy /dev/rtc
> over to the new RTC driver and be done with it.
Initially: because that idea hadn't been suggested. And because that
sort of code migration on PC hardware needs to be done slowly enough
that the migration issues have a real chance to surface. Issues like:
- Change to the ACPI suspend/resume interactions broke RTC wakeup
for a couple releases in the new RTC framework; now fixed.
- HPET stuff. I think the recently merged HPET update may imply
that rtc-cmos needs an HPET hook, but I've not looked at details.
- Minor bugfixes, which have been resolved over time.
- Your desire to keep using old /dev/rtc nodes (no symlink, so new
kernels and old non-udev fileystems can mix). New issue, no patch.
Nothing else come to mind.
> I'd enable it in a
> heartbeat and would encourage distros to do so. Are there missing APIs?
> Is the ioctl API totally different? It's impossible to wrap it?
See above. Once the HPET thing is resolved, I think distros can
convert given some resolution of the /dev/rtc issue.
> I'm not really interested in "this isnt a PC" arguments.
Maybe because for you, it *is* a PC. ;)
> The incompatibility is
> such an obvious migration barrier to me - do you really not see it?
Let's just say that all my PCs run the new code just fine, and not
all of them have /dev/rtc symlinked to /dev/rtc0 ... but I can very
easily imagine it look bit different from a distro perpective.
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