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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> [Fixup year in sysfs ABI documentation] Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Link: https://lore.kernel.org/r/20230818082112.554638-1-anshuman.khandual@arm.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.