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[67.165.245.5]) by smtp.googlemail.com with ESMTPSA id e9e14a558f8ab-3d5d5af8369sm33439725ab.71.2025.04.02.10.42.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Apr 2025 10:42:42 -0700 (PDT) From: Jim Cromie To: jbaron@akamai.com, gregkh@linuxfoundation.org, ukaszb@chromium.org, louis.chauvet@bootlin.com, linux-kernel@vger.kernel.org Cc: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, intel-gvt-dev@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, daniel.vetter@ffwll.ch, tvrtko.ursulin@linux.intel.com, jani.nikula@intel.com, ville.syrjala@linux.intel.com, Jim Cromie , linux-doc@vger.kernel.org Subject: [PATCH v3 29/54] docs/dyndbg: add classmap info to howto Date: Wed, 2 Apr 2025 11:41:31 -0600 Message-ID: <20250402174156.1246171-30-jim.cromie@gmail.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250402174156.1246171-1-jim.cromie@gmail.com> References: <20250402174156.1246171-1-jim.cromie@gmail.com> MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Describe the 3 API macros providing dynamic_debug's classmaps DYNDBG_CLASSMAP_DEFINE - create & export a classmap DYNDBG_CLASSMAP_USE - refer to exported map DYNDBG_CLASSMAP_PARAM - bind control param to the classmap DYNDBG_CLASSMAP_PARAM_REF + use module's storage - __drm_debug TBD: some of this might be over-specification, or just over-talked. NB: The _DEFINE & _USE model makes the user dependent on the definer, just like EXPORT_SYMBOL(__drm_debug) already does. cc: linux-doc@vger.kernel.org Signed-off-by: Jim Cromie --- v3- rework protection around PARAM v0.5 adjustments per Randy Dunlap v0.7 checkpatch fixes v0.8 more v0.9 rewords fixup-howto --- .../admin-guide/dynamic-debug-howto.rst | 93 +++++++++++++++++++ 1 file changed, 93 insertions(+) diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst index 1ceadf4f28f9..5eb4ae3b2f27 100644 --- a/Documentation/admin-guide/dynamic-debug-howto.rst +++ b/Documentation/admin-guide/dynamic-debug-howto.rst @@ -394,3 +394,96 @@ just a shortcut for ``print_hex_dump(KERN_DEBUG)``. For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is its ``prefix_str`` argument, if it is constant string; or ``hexdump`` in case ``prefix_str`` is built dynamically. + +Dynamic Debug classmaps +======================= + +The "class" keyword selects prdbgs based on author supplied, +domain-oriented names. This complements the nested-scope keywords: +module, file, function, line. + +The main difference from the others: classes must be named to be +changed. This protects them from generic overwrite: + + # IOW this cannot undo any DRM.debug settings + :#> ddcmd -p + +This protection is needed in order to honor the ABI, settings done +there must be respected: + + :#> echo 0x1ff > /sys/module/drm/parameters/debug + +So each class must be enabled individually (no wildcards): + + :#> ddcmd class DRM_UT_CORE +p + :#> ddcmd class DRM_UT_KMS +p + # or more selectively + :#> ddcmd class DRM_UT_CORE module drm +p + +That makes direct >control wordy and annoying, but it is a secondary +interface; it is not intended to replace the ABI, just slide in +underneath and reimplement it. + +However, since the param is the ABI, if a classmap DEFINEr doesn't +also add a _CLASSMAP_PARAM, there is no ABI, and no protection is +needed. In that case, class'd prdbgs would be enabled/disabled by +legacy (class-less) queries. + + +Dynamic Debug Classmap API +========================== + +DRM.debug is built upon: + ABI in /sys/module/drm/parameters/debug + the bits set all DRM_UT_* together + ~23 categorized api macros: drm_dbg_() + all calling drm_{,dev}dbg(DRM_UT_*, ....) + ~5000 calls to the api macros across drivers/gpu/drm/* + +The const short ints are good for optimizing compilers; a primary +classmaps design goal was to preserve those opporunities for +optimization. So basically .classid === category. + +Then we use the drm_categories DRM_UT_* enum for both the classnames +(stringified enum symbols) and their numeric values. + +Its expected that future users will also use an enum-defined +categorization scheme like DRM's, and dyndbg can be adapted under them +similarly. + +DYNAMIC_DEBUG_CLASSMAP_DEFINE(var,type,_base,classnames) - this maps +classnames (a list of strings) onto class-ids consecutively, starting +at _base, it also maps the names onto CLASSMAP_PARAM bits 0..N. + +DYNAMIC_DEBUG_CLASSMAP_USE(var) - modules call this to refer to the +var _DEFINEd elsewhere (and exported). + +Classmaps are opt-in: modules invoke _DEFINE or _USE to authorize +dyndbg to update those classes. "class FOO" queries are validated +against the classes, this finds the classid to alter; classes are not +directly selectable by their classid. + +There are 2 types of classmaps: + + DD_CLASS_TYPE_DISJOINT_BITS: classes are independent, like DRM.debug + DD_CLASS_TYPE_LEVEL_NUM: classes are relative, ordered (V3 > V2) + +DYNAMIC_DEBUG_CLASSMAP_PARAM - modelled after module_param_cb, it +refers to a DEFINEd classmap, and associates it to the param's +data-store. This state is then applied to DEFINEr and USEr modules +when they're modprobed. + +The PARAM interface also enforces the DD_CLASS_TYPE_LEVEL_NUM relation +amongst the contained classnames; all classes are independent in the +control parser itself; there is no implied meaning in names like "V4". + +Modules or module-groups (drm & drivers) can define multiple +classmaps, as long as they (all the classmaps) share the limited 0..62 +per-module-group _class_id range, without overlap. If a module +encounters a conflict between 2 classmaps its USEing, we can extend +the _USE macro with an offset to allow avoiding the conflicting range. + +``#define DEBUG`` will enable all pr_debugs in scope, including any +class'd ones. This won't be reflected in the PARAM readback value, +but the class'd pr_debug callsites can be forced off by toggling the +classmap-kparam all-on then all-off.