Re: [PATCH v2 06/28] coresight: etm4x: Add context synchronization before enabling trace

On Wed, Jul 02, 2025 at 12:05:10PM +0100, Yeoreum Yun wrote:

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@@ -445,13 +445,37 @@ static int etm4_enable_trace_unit(struct etmv4_drvdata *drvdata) etm4x_relaxed_write32(csa, TRCRSR_TA, TRCRSR);

etm4x_allow_trace(drvdata);

• /*

• * According to software usage PKLXF in Arm ARM (ARM DDI 0487 L.a),
  

• * execute a Context synchronization event to guarantee the trace unit
  

• * will observe the new values of the System registers.
  

• */
  

• if (!csa->io_mem)

• isb();
  

But, when write to SYS_TRFCR_EL1 in etm4x_allow_trace(), it already does isb(). Is it redundant?

Good point. It is not sufficient. As a system register writing in kvm_tracing_set_el1_configuration(), this is why adds a ISB here.

Thanks, Leo