On Thu, Dec 04, 2025 at 06:27:27PM +0530, Anshuman Khandual wrote:

On 01/12/25 4:51 PM, Leo Yan wrote:

quoted

If the driver does not clear the status when disabling the trace buffer
unit, stale state will carry over to the next enable, though the driver
clears it again on enable.

There is no problem now ! Because trbe_enable_hw() calls clr_trbe_status().

quoted

Explicitly clear status after the trace is disabled in the interrupt
handling and when a perf session ends.  Keep the status for spurious
interrupts for continuous tracing.

But is not that the behaviour already without this change ?

clr_trbe_status() in trbe_enable_hw() ensures that no TRBE session can be
started without first clearing the existing status. Still wondering what
is the purpose of this change ?

It is about the driver's sanity.

The driver should clear the status immediately when the trace unit is
disabled, rather than waiting until the next enable.  This avoids
unexpected behaviour, such as a spurious TRBE interrupt.

Consider an edge case: if TRBE is being disabled at the same moment it
is about to raise an interrupt, arm_trbe_update_buffer() may miss the
IRQ bit due to latency.  If arm_trbe_disable() does not clear that bit,
arm_trbe_irq_handler() will still run after the perf event has been
stopped.  The interrupt handler then retrieves the trbe_buf pointer
from the perf output handle, which is dangerous because the perf
session has already ended.

Thanks,
Leo