On Wed, 26 Nov 2025 at 15:33, James Clark james.clark@linaro.org wrote:
On 26/11/2025 1:42 pm, Mike Leach wrote:
Hi,
On Wed, 26 Nov 2025 at 12:31, Leo Yan leo.yan@arm.com wrote:
On Wed, Nov 26, 2025 at 12:11:05PM +0000, James Clark wrote:
[...]
This fix can still be applied to older kernels, but seems to me that now might be an appropriate time to consider removing the ETMv3 driver from the mainline kernel?
Yeah, if anyone is using it it would be on an old kernel surely?
We can confirm this in another way: if I don't miss anything, over the past several years (since 2017), we have not received any questions or bug reports based on hands-on practice regarding ETMv3 on the Coresight or perf mailing lists.
Thanks, Leo
The key to this is not the questions we are asked, but which platforms are still supported by the linux kernel.
The ETMv3 driver supports both ETMv3 and PTM trace (the programming model is the same, even if the trace decode is vastly different).
So as long as there are platforms supported that use either of those, we need to keep the driver in.
Mike
We're not running tests though, so if we find out it's fundamentally broken somehow it could be another justification to remove it, even if the kernel supports the devices. Do you have a board that you can test on Mike?
Don't have one myself, but I believe the TC2 was used in development, (that's the A15/A7 32 bit part - not total compute!) which somewhat conveniently had both etmv3 and ptm trace.
Maintenance hasn't been zero cost either, even build testing for arm32 is annoying enough.
Pretty much the seem for any of the arm32 drivers I guess.
Until arm32 kernels are no longer supported, not sure it is safe to drop the etm3 driver as we do not know who out there might be using it.
Mike
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK