[PATCH AUTOSEL 6.16-6.1] MIPS: lantiq: falcon: sysctrl: fix request memory check logic

[Sasha Levin <sashal@kernel.org>]

From: Shiji Yang <yangshiji66@outlook.com>

[ Upstream commit 9c9a7ff9882fc6ba7d2f4050697e8bb80383e8dc ]

request_mem_region() will return NULL instead of error code
when the memory request fails. Therefore, we should check if
the return value is non-zero instead of less than zero. In
this way, this patch also fixes the build warnings:

arch/mips/lantiq/falcon/sysctrl.c:214:50: error: ordered comparison of pointer with integer zero [-Werror=extra]
  214 |                                 res_status.name) < 0) ||
      |                                                  ^
arch/mips/lantiq/falcon/sysctrl.c:216:47: error: ordered comparison of pointer with integer zero [-Werror=extra]
  216 |                                 res_ebu.name) < 0) ||
      |                                               ^
arch/mips/lantiq/falcon/sysctrl.c:219:50: error: ordered comparison of pointer with integer zero [-Werror=extra]
  219 |                                 res_sys[0].name) < 0) ||
      |                                                  ^
arch/mips/lantiq/falcon/sysctrl.c:222:50: error: ordered comparison of pointer with integer zero [-Werror=extra]
  222 |                                 res_sys[1].name) < 0) ||
      |                                                  ^
arch/mips/lantiq/falcon/sysctrl.c:225:50: error: ordered comparison of pointer with integer zero [-Werror=extra]
  225 |                                 res_sys[2].name) < 0))
      |

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

**YES**

This commit should be backported to stable kernel trees. Here's my
extensive analysis:

## Bug Fix Nature

This commit fixes a **genuine logic error** in the error checking of
`request_mem_region()` calls. The function returns a pointer
(specifically `struct resource *`) on success and NULL on failure, not
an error code. The original code was incorrectly checking if the return
value was `< 0`, which is inappropriate for pointer comparisons.

## Specific Code Analysis

1. **Original broken code** (lines 213-225 in the diff):
   - Used `< 0` comparison with pointer return values
   - This is fundamentally wrong as `request_mem_region()` returns
     `struct resource *` or NULL
   - The broken check would never trigger because pointers are unsigned
     values

2. **Fixed code**:
   - Correctly checks for NULL by negating the return value
     (`!request_mem_region(...)`)
   - This properly detects when memory region requests fail

## Impact Assessment

1. **Functional Impact**: The bug could lead to the kernel continuing
   execution even when critical memory regions couldn't be reserved,
   potentially causing:
   - Resource conflicts
   - System instability on Lantiq Falcon MIPS platforms
   - Unpredictable behavior when accessing unreserved memory regions

2. **Build Impact**: The commit also fixes compiler warnings with
   `-Werror=extra`, which could break builds with strict warning
   settings

3. **Scope**: The fix is:
   - Small and contained (only changes error checking logic)
   - Architecture-specific (MIPS Lantiq Falcon)
   - Low risk of introducing regressions
   - Simple logical correction without algorithmic changes

## Stable Tree Criteria

This commit meets key stable tree requirements:
- **Fixes a real bug**: Incorrect error handling that could lead to
  system issues
- **Small change**: Only modifies the comparison logic, no structural
  changes
- **Clear fix**: The correction is obvious and verifiable
- **No new features**: Pure bug fix
- **Minimal risk**: The fix is straightforward and correct
- **Important for affected systems**: Lantiq Falcon platforms need
  proper resource management

The commit is an ideal candidate for stable backporting as it fixes a
clear programming error that affects system stability without
introducing complexity or risk.

 arch/mips/lantiq/falcon/sysctrl.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/arch/mips/lantiq/falcon/sysctrl.c b/arch/mips/lantiq/falcon/sysctrl.c
index 1187729d8cbb..357543996ee6 100644
--- a/arch/mips/lantiq/falcon/sysctrl.c
+++ b/arch/mips/lantiq/falcon/sysctrl.c
@@ -214,19 +214,16 @@ void __init ltq_soc_init(void)
 	of_node_put(np_syseth);
 	of_node_put(np_sysgpe);
 
-	if ((request_mem_region(res_status.start, resource_size(&res_status),
-				res_status.name) < 0) ||
-		(request_mem_region(res_ebu.start, resource_size(&res_ebu),
-				res_ebu.name) < 0) ||
-		(request_mem_region(res_sys[0].start,
-				resource_size(&res_sys[0]),
-				res_sys[0].name) < 0) ||
-		(request_mem_region(res_sys[1].start,
-				resource_size(&res_sys[1]),
-				res_sys[1].name) < 0) ||
-		(request_mem_region(res_sys[2].start,
-				resource_size(&res_sys[2]),
-				res_sys[2].name) < 0))
+	if ((!request_mem_region(res_status.start, resource_size(&res_status),
+				 res_status.name)) ||
+	    (!request_mem_region(res_ebu.start, resource_size(&res_ebu),
+				 res_ebu.name)) ||
+	    (!request_mem_region(res_sys[0].start, resource_size(&res_sys[0]),
+				 res_sys[0].name)) ||
+	    (!request_mem_region(res_sys[1].start, resource_size(&res_sys[1]),
+				 res_sys[1].name)) ||
+	    (!request_mem_region(res_sys[2].start, resource_size(&res_sys[2]),
+				 res_sys[2].name)))
 		pr_err("Failed to request core resources");
 
 	status_membase = ioremap(res_status.start,
-- 
2.39.5