On 04/12/2025 1:45 pm, Mike Leach wrote:
Hi,
On Thu, 4 Dec 2025 at 10:55, James Clark james.clark@linaro.org wrote:
On 02/12/2025 11:53 am, James Clark wrote:
On 02/12/2025 11:43 am, Leo Yan wrote:
On Mon, Dec 01, 2025 at 04:41:07PM +0000, Coresight ML wrote:
[...]
@@ -746,7 +779,7 @@ static void cs_etm_get_metadata(struct perf_cpu cpu, u32 *offset, case CS_ETMV3: magic = __perf_cs_etmv3_magic; /* Get configuration register */
info->priv[*offset + CS_ETM_ETMCR] = cs_etm_get_config(itr);
info->priv[*offset + CS_ETM_ETMCR] = cs_etm_guess_etmcr(itr);I still think cs_etm_get_config() is better than cs_etm_guess_etmcr().
For ETMv3, we directly pass CONFIG to the kernel, and after validation in the dirver, then the value will be set to ETMCR. If we already know the config value is consistent between user space and kernel, why
One other note is that since moving the timestamp field, this is no longer true either. The value in attr.config isn't directly put into ETMCR.
introduce a redundant "guess" operation here?
Thanks, Leo
Because userspace doesn't always come up with the same value as the driver. For example right now in ETM3, ETMCR_RETURN_STACK isn't set depending on certain conditions that userspace doesn't know about. ETM4 has the same for TRCCONFIGR_RS and maybe some others. In the future, other versions of the driver could do different things as long as we don't break decoding.
I didn't want the function name to imply it was doing something it wasn't as that confused me a little bit. It's definitely not "getting" the value. Maybe "guess" isn't the best it could be, but it's not far off.
Perhaps cs_etm_synth_etmcr()? We cannot read it directly as it has not
synth is a good name, I can use that.
been set at the time of creating these headers. (unlike the sets of static read only IDR regs that we do read).
When in perf mode the only configuration bits set in the ConfigR for either ETM3 or 4 are those generated or implied by parameters on the perf command line. This info has to pass from perf to the driver somehow. Evidently many years ago, when only ETMv3/PTM existed the easy way was perf.config == etm.configr, now that is no longer feasible. As long as perf and the drivers interpret the command line attributes in the same way - all is well.
As James says, the actual configr can differ from the synth one - the key is the bits that control the trace format - e.g. cyclecounts, rather than trace filtering e.g. userspace/kernel that affects the drivers configr but not the synthesized value in perf. Decode cares about format, not about filtering. Additionally some things - like return-stack are implementation dependent - optional on PTM, not at all on ETMv3. If the trace unit does not support it then the drivers ignore this. the only effect on the trace output is less compression if retstack cannot be used.
Generally decode needs to know about things that affect format and function, rather than filtering.
Mike