qconfig: Allow searching for CONFIG values

Add basic support for searching for matching of non-matching values.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: https://source.denx.de/u-boot/custodians/u-boot-dm/-/issues/20

doc/develop/qconfig.rst

@@ -85,6 +85,20 @@ example, to find boards which enabled CONFIG_SCSI but not CONFIG_BLK::
     3 matches
     pg_wcom_seli8_defconfig highbank_defconfig pg_wcom_expu1_defconfig
 
+It is also possible to search for particular values. For example, this finds all
+boards with an empty string for `CONFIG_DEFAULT_FDT_FILE`::
+
+    ./tools/qconfig.py -f DEFAULT_FDT_FILE=\"\"
+    1092 matches
+    ...
+
+This finds boards which have a value for SYS_MAXARGS other than 64::
+
+    ./tools/qconfig.py -f ~SYS_MAXARGS=64
+    cfg CONFIG_SYS_MAXARGS
+    281 matches
+    ...
+
 
 Finding implied CONFIGs
 -----------------------

tools/qconfig.py

@@ -1079,7 +1079,7 @@ def do_imply_config(config_list, add_imply, imply_flags, skip_added,
             for linenum in sorted(linenums, reverse=True):
                 add_imply_rule(config[CONFIG_LEN:], fname, linenum)
 
-def defconfig_matches(configs, re_match):
+def defconfig_matches(configs, re_match, re_val):
     """Check if any CONFIG option matches a regex
 
     The match must be complete, i.e. from the start to end of the CONFIG option.
@@ -1089,12 +1089,14 @@ def defconfig_matches(configs, re_match):
             key: CONFIG option
             value: Value of option
         re_match (re.Pattern): Match to check
+        re_val (re.Pattern): Regular expression to check against value (or None)
 
     Returns:
         bool: True if any CONFIG matches the regex
     """
-    for cfg in configs:
+    for cfg, val in configs.items():
         if re_match.fullmatch(cfg):
+            if not re_val or re_val.fullmatch(val):
                 return True
     return False
 
@@ -1123,6 +1125,11 @@ def do_find_config(config_list):
         if cfg[0] == '~':
             want = False
             cfg = cfg[1:]
+        val = None
+        re_val = None
+        if '=' in cfg:
+            cfg, val = cfg.split('=', maxsplit=1)
+            re_val = re.compile(val)
 
         # Search everything that is still in the running. If it has a config
         # that we want, or doesn't have one that we don't, add it into the
@@ -1131,7 +1138,7 @@ def do_find_config(config_list):
         out = set()
         re_match = re.compile(cfg)
         for defc in in_list:
-            has_cfg = defconfig_matches(config_db[defc], re_match)
+            has_cfg = defconfig_matches(config_db[defc], re_match, re_val)
             if has_cfg == want:
                 out.add(defc)
     print(f'{len(out)} matches')