On 10 Sep 01, Loïc Minier wrote:
On Wed, Sep 01, 2010, Amit Kucheria wrote:
That patch likely won't go upstream.
Why not?
Because it adds a sub-arch, revision-specific override into generic architecture code (vfpmodule.c)
To do this elegantly with a hope to get it to mainline, we'd need a way to disable the hwcap through some board-specific fixup code that can check the revision of the board at runtime.
Unfortunately, it seems after talking to Nicolas that mdesc->fixup() is called too early.
Nicolas suggested linking the i.MX5 code _after_ the VFP module :)
OTOH, how important is support below TO3?
For Linaro, not too important I guess, some people have TO2 hardware, some Babbage 2.0 or 2.5, albeit 2.0 is not really supported anymore. EfikaMX also comes in both TO2 and TO3. Finally, some mass-market / public hardware like Sharp Netwalker are TO2 based.
TO1 won't even boot on Freescale's BSP, IIRC. AFAICT, Freescale isn't testing their BSP on TO2 if you take into account bugs like LP # 615722 [1] that caused bricking of Babbage 2.5 boards. And new HW is all TO3 and so is all known production HW. We only have a few TO2 boards now those will get rapidly get discarded when we get newer ones.
Some months back, in the beginning of this year, I heard of commercial projects targetting TO2 to save some money on the chip. There's also some mass-market / public TO2 hardware in the form of the netwalker.
I hope they didn't get bitten by the bricking problems.
So, IMHO, enable NEON support and add to release-notes that TO1/2 is not supported.
We can do that in Linaro, I'm just a bit uncomfortable that there is a non-trivial amount of TO2 devices out there, and it's a DoS issue to have this NEON flaw.
I would be ok if we would only support TO3 and the kernel wouldn't boot on TO2 hardware, but AIUI the kernel will boot just fine and turn on NEON on TO2 such as Babbage 2.x, so I'm a bit scared by just release noting it.
Another solution is that we could perhaps add code in the board init function to check the cpu revision and if NEON was enabled, then stop booting.
/Amit