Mitch Bradley wrote:
Mike Rapoport wrote:
Mitch Bradley wrote:
Mike Rapoport wrote:
Mitch Bradley wrote:
The second topic is the hypothetical use of OFW as a HAL. That will
not happen for several reasons. The opposition to the idea is
widespread and deeply held, and there are good arguments to support
that opposition. Furthermore, the economic conditions necessary
for the creation of such a HAL do not exist in the ARM world, nor
indeed in the Linux world in general. (The necessary condition is
the ability for one company to impose a substantial change by fiat
- essentially a monopoly position.)
Shall we agree, then, that any further discussion of the HAL issue
is "just for fun", and that nobody needs to feel threatened that it
would actually happen?
I've recently worked with vendor versions of U-Boot for advanced ARM
SoCs. There is already *huge* chunk of HAL code in those versions.
And if there would be possibility to have callbacks into the
firmware these chunks would only grow, IMHO.
How can there be HAL code in U-Boot unless there is already the
possibility to have callbacks into the firmware?
Currently it aims to abstract hardware from U-Boot and reuse the same
HW access code across operating systems and bootloaders. If this code
would have callbacks I afraid the things would became worse.
The only way I can understand what you said is if I assume that by
"callback", you mean the following sequence:
a) U-boot loads and executes the OS, providing to the OS the address of
some HW access routines that it can use
b) The OS calls one of those HW access routines
c) During the execution of that HW access routine, that routine calls
"back" into the OS, before returning. So a call into the OS is nested
inside a call into U-boot resident code.
If that is what you are worried about, it is not what we were
discussing. We were discussing - and many people were against - step (b).
Are you saying that step (b) - the OS calling into routines provided by
U-Boot - is already the status quo?
I'm also objecting the step (b) and, fortunately, it's not yet the
status quo.
Current U-Boot/kernel implementations I've encountered still do not have
OS calls to resident HW access routines. But if such calls would be
allowed, my impression is that SoC vendors would make extensive use of them.
It is not HAL if it can't be called.
The potential for "vendors breaking out of the debugging use case
and turning it into a HAL" is miniscule, because
a) The callback is disabled by default
b) The technical challenges of the callback interface limit its
applicability to specific "wizard user" scenarios
c) OFW is unlikely to achieve sufficient market penetration for the
HAL thing to be worth doing
_______________________________________________
linux-arm-kernel mailing list
linux-arm-ker...@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
--
Sincerely yours,
Mike.
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
