On 17 May 2014, at 10:46, Russell King - ARM Linux <li...@arm.linux.org.uk> wrote: > On Sat, May 17, 2014 at 10:23:37AM +0100, Catalin Marinas wrote: >> On Fri, May 16, 2014 at 01:55:46PM +0100, Russell King - ARM Linux wrote: >>> There was a CPU called the ARM710, it was ARMv3 and it had no Thumb support. >>> >>> There is also a CPU called the ARM710T, which is ARMv4 and has Thumb >>> support. >>> >>> These are two completely different CPUs, the former was removed along with >>> the removal of ARMv3 support. The latter remains because we still support >>> ARMv4. >> >> BTW, while clearly this patch was removing code for the wrong reasons, I >> think we should set a longer term timeline for getting rid of some of >> old features. Let's say in 10 years time we remove everything ARMv4, >> another 10 years ARMv5 and so on. We could make these milestones shorter >> but it really depends on what people use, we should not force them out >> of the kernel if still in use. > > I still use StrongARM based machines here, and I don't see that changing > unless some suitably designed ARM boards come my way which (a) offer the > same features and (b) out perform it. > > The problem is that there's lots of ARM boards which satisfy (b) - the > iMX6 stuff clearly does - but hardly anything which satisfies (a). > > There's also been some recent effort with SA1100 SoC code, so there's > also other interest there still. > > So, ARMv4 is still very much in use with modern kernels.
That’s why I said maybe aim for removing it in 10 year. But if code is still in use by that time, we keep it. > The difference between what you're proposing and what happened to ARMv3 > is that ARMv3 was broken for quite some time (we read from some of the > CP15 registers which are read-only in ARMv3) and no one ever raised a > problem with that. So, after a sufficient period of time, it got removed > - and no one batted an eyelid. That's the correct way to do it - allow > code to age, and if no one notices it's been broken, then it can be > removed. I’m more for pro-actively “breaking” it with a DEPRECATED dependency. For example, if you suspect that some code like ARM710T is no longer in use, we mark it and see if anyone complains about this over a two years period. If not, it gets removed. Waiting for code to get broken is another way but it’s less predictable. Catalin-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
