linux-kernel - [RFC PATCH 03/17] dyndbg: fix readback value on LEVEL

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Message-Id: <20221206003424.592078-4-jim.cromie@gmail.com>
Date:   Mon,  5 Dec 2022 17:34:10 -0700
From:   Jim Cromie <jim.cromie@...il.com>
To:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org, intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org
Cc:     jani.nikula@...el.com, ville.syrjala@...ux.intel.com,
        daniel.vetter@...ll.ch, seanpaul@...omium.org, robdclark@...il.com,
        jbaron@...mai.com, gregkh@...uxfoundation.org,
        Jim Cromie <jim.cromie@...il.com>
Subject: [RFC PATCH 03/17] dyndbg: fix readback value on LEVEL_NAMES interfaces

Since sysfs knobs should generally read-back what was just written
(unless theres a good reason to do otherwise), this result (using
test_dynamic_debug.ko) is suboptimal:

  echo L3 > p_level_names
  cat p_level_names
  4

Fix this with a -1 offset in LEVEL_NAMES readback.

NOTE:

Calling this a BUG is debatable, and the above is slightly inaccurate
wrt "read-back"; whats written is a LEVEL_NAME (a string).  Whats read
back is an integer, giving the 'edge' of the 'low-pass-filter'

The actual test looks like:

RTT: L4 -> p_level_names : 4 :: DOING: levels 4-1
[   17.509594] dyndbg: "L4" > p_level_names:0x4
[   17.510115] dyndbg: apply: 0x1f to: 0xf
[   17.510506] dyndbg: query 0: "class L4 +p" mod:*
[   17.510992] dyndbg: split into words: "class" "L4" "+p"
[   17.511521] dyndbg: op='+'
[   17.511811] dyndbg: flags=0x1
[   17.512127] dyndbg: *flagsp=0x1 *maskp=0xffffffff
[   17.512604] dyndbg: parsed: func="" file="" module="" format="" lineno=0-0 class=L4
[   17.513414] dyndbg: applied: func="" file="" module="" format="" lineno=0-0 class=L4
[   17.514204] dyndbg: processed 1 queries, with 1 matches, 0 errs
[   17.514809] dyndbg: bit_4: 1 matches on class: L4 -> 0x1f
[   17.515355] dyndbg: p_level_names: changed bit-4: "L4" f->1f
[   17.515933] dyndbg: total matches: 1
crap [[ 5 != 4 ]]

This -1 adjustment just reports the edge consistently with its
input-mapping.

Fixes: b9400852c080 (dyndbg: add drm.debug style (drm/parameters/debug) bitmap support)

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 lib/dynamic_debug.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 009f2ead09c1..48ca1387a409 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -794,6 +794,8 @@ int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp)
 		return scnprintf(buffer, PAGE_SIZE, "0x%lx\n", *dcp->bits);
 
 	case DD_CLASS_TYPE_LEVEL_NAMES:
+		return scnprintf(buffer, PAGE_SIZE, "%d\n", *dcp->lvl - 1);
+
 	case DD_CLASS_TYPE_LEVEL_NUM:
 		return scnprintf(buffer, PAGE_SIZE, "%d\n", *dcp->lvl);
 	default:
-- 
2.38.1