On 05/23/2016 01:56 PM, Lorenzo Pieralisi wrote:

On Tue, May 17, 2016 at 12:48:53PM -0400, Jon Masters wrote:

quoted

On 05/17/2016 12:44 PM, Jon Masters wrote:

quoted

1). During development of a platform, it is much easier to debug
problems with tables if you can test replacement ones without having to
respin the firmware. In the server world, you usually don't have the
firmware source code, so to get it respun could be days-weeks even if
you are working with the authors closely. We have practically used this
feature on a number of platforms already and it will continue.

For example, on one platform we were unable to fully boot RHEL(SA) due
to a bug in one of the ACPI tables. But I was able to boot the system to
a ramdisk containing a uuencode library and then write out the content
of the tables over the serial port, then decompile/patch/recompile, and
override replacement tables on the system. Then we beat the vendor up
with the fixes and the official firmware was corrected.

Can you explain to me please why you can't do it with GRUB ?

It's doable with GRUB (if you rebuild GRUB modules to include it)

I am using mainline GRUB and its acpi command all the time to update
static ACPI tables for testing new features (ie IORT) and it works
just fine for me (and you can still override the DSDT, which is
likely to be the main source of bugs, through the CONFIG_ACPI_CUSTOM_DSDT
config option, that works on ARM in mainline with no changes required).

I just want to understand if there is really a compelling reason
for adding this stuff when we can easily implement its features
through something that is usable today without any kernel changes.

We're looking for x86 feature parity in the base platform. Every time
there's a gratuitous differentiation it's a waste of time for folks
trying to figure out what is different on an ARM system. So if we
completely remove the ACPI override feature from the kernel and make
everyone use GRUB instead, then fine, but ARM shouldn't be special.

Jon.

-- 
Computer Architect | Sent from my Fedora powered laptop