powerpc: Remove flag CTLFLAG_TUN from sysctl knob hw.platform

[zlei]

Summary

Prior to change [1] this flag is useless but harmless. After the change
plat_name[] will be fetched from kernel environment after invoking the
platform probe function platform_probe_and_attach(). The probe function
runs at early boot stage prior to mi_startup() thus it is too late and
pointless to set plat_name[].

Nathan mentioned that the logic to specify the platform pre-dates the
powerpc64 work, and is from the original pre-FDT Book-E bringup from
like 2008. So it's irrelevant these days. Let's clean it up now.

[1] 3da1cf1e88f8 Extend the meaning of the CTLFLAG_TUN flag to ...

MFC after: 3 days

[zlei]

sys/powerpc/powerpc/platform.c

369

Any real usage to requested the platform via loader tunable ?

[olce]

Seems fine to me, but I'm not a PowerPC specialist.

[jhibbits]

sys/powerpc/powerpc/platform.c

369

I highly doubt it. It might be more useful on, say, the Book-E side, where qemu may not pass a 'correct' device tree, but other than that I don't see a need for this anymore. My guess is it was added while Nathan was working on the powerpc64 bringup, so he could coerce things. It's very likely unused by this point.

[nwhitehorn]

I think it actually pre-dates the powerpc64 work, and is from the original pre-FDT Book-E bringup from like 2008. It's for sure irrelevant these days.

[zlei]

sys/powerpc/powerpc/platform.c

348

In D48897#1115405, @nwhitehorn wrote:

I think it actually pre-dates the powerpc64 work, and is from the original pre-FDT Book-E bringup from like 2008. It's for sure irrelevant these days.

Then this is actually not needed now, right ? And the following logic

		/*
		 * Check if this module was specifically requested through
		 * the loader tunable we provide.
		 */
		if (strcmp(platp->name,plat_name) == 0) {
			plat_def_impl = platp;
			break;
		}

becomes dead ( well actually has been dead for quite a long time ).

I see ps3 is fetching from kenv,

sys/powerpc/ps3/ps3_syscons.c:	TUNABLE_STR_FETCH("hw.platform", compatible, sizeof(compatible));

to determin the VT driver ( as a fallback IIUC ). If that is field for debugging / developing, I'd suggest to remove the CTLFLAG_TUN from the sysctl knob hw.platfrom , so we do not attempt user to hack it. Well the dead code can also be removed, but I'll let it up to you @nwhitehorn to decide.

@jhibbits @nwhitehorn How do you think ?

[nwhitehorn]

In D48897#1115523, @zlei wrote:

I think removing everything is fine. The PS3 code is from the very misty past where the PS3 didn't have FDTs (as all of of this is), but that circumstance has been gone for a decade. The set of people who use FreeBSD on PS3 is probably at most one or two at this point, also.

[zlei]

Removed sysctl flag CTLFLAG_TUN. Removed now irrelevant code.

[zlei]

Friendly ping .