Re: [PATCH V2] coresight: tmc: Make etr buffer mode user configurable from sysfs

From: Anshuman Khandual <anshuman.khandual@arm.com>
To: linux-arm-kernel@lists.infradead.org, suzuki.poulose@arm.com
Cc: Mike Leach <mike.leach@linaro.org>,
	James Clark <james.clark@arm.com>, Leo Yan <leo.yan@linaro.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	coresight@lists.linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2] coresight: tmc: Make etr buffer mode user configurable from sysfs
Date: Fri, 15 Sep 2023 15:23:20 +0530	[thread overview]
Message-ID: <56db2f8b-23c6-a664-7c8b-4c000449abe1@arm.com> (raw)
In-Reply-To: <20230818082112.554638-1-anshuman.khandual@arm.com>

On 8/18/23 13:51, Anshuman Khandual wrote:
> Currently TMC-ETR automatically selects the buffer mode from all available
> methods in the following sequentially fallback manner - also in that order.
> 
> 1. FLAT mode with or without IOMMU
> 2. TMC-ETR-SG (scatter gather) mode when available
> 3. CATU mode when available
> 
> But this order might not be ideal for all situations. For example if there
> is a CATU connected to ETR, it may be better to use TMC-ETR scatter gather
> method, rather than CATU. But hard coding such order changes will prevent
> us from testing or using a particular mode. This change provides following
> new sysfs tunables for the user to control TMC-ETR buffer mode explicitly,
> if required. This adds following new sysfs files for buffer mode selection
> purpose explicitly in the user space.
> 
> /sys/bus/coresight/devices/tmc_etr<N>/buf_modes_available
> /sys/bus/coresight/devices/tmc_etr<N>/buf_mode_preferred
> 
> $ cat buf_modes_available
> auto flat tmc-sg catu	------------------> Supported TMC-ETR buffer modes
> 
> $ echo catu > buf_mode_preferred   -------> Explicit buffer mode request
> 
> But explicit user request has to be within supported ETR buffer modes only.
> These sysfs interface files are exclussive to ETR, and hence these are not
> available for other TMC devices such as ETB or ETF etc.
> 
> A new auto' mode (i.e ETR_MODE_AUTO) has been added to help fallback to the
> existing default behaviour, when user provided preferred buffer mode fails.
> ETR_MODE_FLAT and ETR_MODE_AUTO are always available as preferred modes.
> 
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: James Clark <james.clark@arm.com>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: coresight@lists.linaro.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> This applies on v6.5-rc6
> 
> Changes in V2:

Hi Suzuki,

This patch still applies cleanly on current coresight/for-next/queue.
But in case, this needs any changes, please do let me know. Thanks !

- Anshuman