linux-kernel - Re: [PATCH] coresight-tmc: Add configurable timeout for flush and tmcready

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Message-ID: <20250627141745.GS794930@e132581.arm.com>
Date: Fri, 27 Jun 2025 15:17:45 +0100
From: Leo Yan <leo.yan@....com>
To: James Clark <james.clark@...aro.org>
Cc: Yuanfang Zhang <quic_yuanfang@...cinc.com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>, kernel@....qualcomm.com,
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: Re: [PATCH] coresight-tmc: Add configurable timeout for flush and
 tmcready

On Fri, Jun 27, 2025 at 12:23:29PM +0100, James Clark wrote:
> 
> 
> On 27/06/2025 12:10 pm, Yuanfang Zhang wrote:
> > The current implementation uses a fixed timeout via
> > coresight_timeout(), which may be insufficient when multiple
> > sources are enabled or under heavy load, leading to TMC
> > readiness or flush completion timeout.
> > 
> > This patch introduces a configurable timeout mechanism for
> > flush and tmcready.
> > 
> 
> What kind of values are you using? Is there a reason to not increase the
> global one?

IIUC, this patch is related to patch [1].

It seems to me that both patches aim to address the long latency when
flushing the TMC, but take different approaches. In the earlier patch,
both Mike and I questioned how the timeout occurred in hardware, but
no information provided about the cause.

I would suggest that we first make clear if this is a hardware quirk or
a common issue in Arm CoreSight.

Thanks,
Leo

[1] https://lore.kernel.org/linux-arm-kernel/CAJ9a7Vgre_3mkXB_xeVx5N9BqPTa2Ai4_8E+daDZ-yAUv44A9g@mail.gmail.com/