[PATCH i-g-t v2 3/5] lib: Preserve string const qualifiers

[Alex Hung <alex.hung@amd.com>]

With glibc 2.43, string searches on const input return const pointers.
Storing these results in char * variables causes compiler warnings.

The following warning is observed on Ubuntu 26.04 (wrapped):

  ../lib/igt_drm_fdinfo.c: In function 'parse_region':
  ../lib/igt_drm_fdinfo.c:122:4: warning:
    assignment discards 'const' qualifier from pointer target type
    [-Wdiscarded-qualifiers]

Use const char * for read-only search results and preserve const in
igt_get_dc6_counter() and its callers. Give strtoull() a separate
end pointer in the fdinfo parser so its input pointer can remain
const without a cast.

Assisted-by: Copilot:GPT-6-Astra
Signed-off-by: Alex Hung <alex.hung@amd.com>
---
 lib/i915/i915_dp.c   |  2 +-
 lib/igt_core.c       |  2 +-
 lib/igt_drm_fdinfo.c |  7 ++++---
 lib/igt_pm.c         | 10 +++++-----
 lib/igt_pm.h         |  2 +-
 5 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/lib/i915/i915_dp.c b/lib/i915/i915_dp.c
index 3d570f7cc..595010140 100644
--- a/lib/i915/i915_dp.c
+++ b/lib/i915/i915_dp.c
@@ -49,7 +49,7 @@
  */
 static int i915_dp_parse_marked_value(const char *buf, char marked_char, int *result)
 {
-	char *marked_ptr, *val_ptr;
+	const char *marked_ptr, *val_ptr;
 
 	/*
 	 * Look for the marked character
diff --git a/lib/igt_core.c b/lib/igt_core.c
index d5dc5324d..b1d045161 100644
--- a/lib/igt_core.c
+++ b/lib/igt_core.c
@@ -1141,7 +1141,7 @@ static int common_init(int *argc, char **argv,
 
 	/* Check for conflicts and calculate space for passed-in extra long options */
 	for  (extra_opt_count = 0; extra_long_opts && extra_long_opts[extra_opt_count].name; extra_opt_count++) {
-		char *conflicting_char;
+		const char *conflicting_char;
 
 		/* check for conflicts with standard long option values */
 		for (i = 0; long_options[i].name; i++) {
diff --git a/lib/igt_drm_fdinfo.c b/lib/igt_drm_fdinfo.c
index 74a90c437..056eb2ca8 100644
--- a/lib/igt_drm_fdinfo.c
+++ b/lib/igt_drm_fdinfo.c
@@ -114,7 +114,8 @@ static int parse_region(const char *name, struct drm_client_fdinfo *info,
 			const char **region_map, unsigned int region_entries,
 			uint64_t *val)
 {
-	char *p;
+	const char *p;
+	char *end;
 	ssize_t name_len;
 	int found = -1;
 	unsigned int i;
@@ -160,8 +161,8 @@ static int parse_region(const char *name, struct drm_client_fdinfo *info,
 		goto out;
 
 	p++;
-	*val = strtoull(p, &p, 10);
-	p = (char *)ignore_space(p);
+	*val = strtoull(p, &end, 10);
+	p = ignore_space(end);
 	if (!*p)
 		goto out;
 
diff --git a/lib/igt_pm.c b/lib/igt_pm.c
index 7905deb8d..1e3cc7757 100644
--- a/lib/igt_pm.c
+++ b/lib/igt_pm.c
@@ -1555,7 +1555,7 @@ uint32_t igt_get_dc_counter(const char *dc_data)
 {
 	char *e;
 	long ret;
-	char *s = strchr(dc_data, ':');
+	const char *s = strchr(dc_data, ':');
 
 	igt_assert(s);
 	s++;
@@ -1586,9 +1586,9 @@ bool igt_support_dc6(int debugfs_fd)
  *
  * Searches for DC6 counter information in the DMC info buffer.
  */
-char *igt_get_dc6_counter(const char *buf)
+const char *igt_get_dc6_counter(const char *buf)
 {
-	char *str;
+	const char *str;
 
 	str = strstr(buf, "DC5 -> DC6 count");
 	if (!str)
@@ -1607,7 +1607,7 @@ char *igt_get_dc6_counter(const char *buf)
 uint32_t igt_read_dc_counter(int debugfs_fd, int dc_flag)
 {
 	char buf[4096];
-	char *str;
+	const char *str;
 
 	igt_debugfs_simple_read(debugfs_fd, "i915_dmc_info", buf, sizeof(buf));
 
@@ -1669,7 +1669,7 @@ const char *igt_dc_state_name(int dc_flag)
  */
 void igt_require_dc_counter(int debugfs_fd, int dc_flag)
 {
-	char *str;
+	const char *str;
 	char buf[4096];
 
 	igt_debugfs_simple_read(debugfs_fd, "i915_dmc_info",
diff --git a/lib/igt_pm.h b/lib/igt_pm.h
index cd9dceb1e..328875f9c 100644
--- a/lib/igt_pm.h
+++ b/lib/igt_pm.h
@@ -108,7 +108,7 @@ bool igt_has_pci_pm_capability(struct pci_device *pci_dev);
 void igt_pm_dpms_toggle(igt_output_t *output);
 uint32_t igt_get_dc_counter(const char *dc_data);
 bool igt_support_dc6(int debugfs_fd);
-char *igt_get_dc6_counter(const char *buf);
+const char *igt_get_dc6_counter(const char *buf);
 uint32_t igt_read_dc_counter(int debugfs_fd, int dc_flag);
 bool igt_dc_state_wait_entry(int debugfs_fd, int dc_flag, int prev_dc_count);
 const char *igt_dc_state_name(int dc_flag);
-- 
2.53.0