[PATCH 1/1] sparc64: unify thread stack sizing and add explicit 32KB stack

[Tony Rodriguez <unixpro1970@gmail.com>]

This patch restructures the thread‑stack sizing logic into a single
if / elif / else chain and introduces an explicit 32KB kernel stack
for SPARC64. The previous implementation relied on nested conditionals
and PAGE_SHIFT‑dependent behavior, which produced 8KB or 16KB stacks
depending on configuration. SPARC64 requires a larger,
architecture‑specific stack due to its trapframe size, register‑window
behavior, and deeper call paths.

A reproducible failure case occurs when usbcore is enabled: USB hub
enumeration (usb_new_device(), hub_port_connect(), PM/QoS helpers)
allocates large on‑stack structures and recurses through several
layers of device‑model code. Combined with SPARC64’s trapframe and
register‑window overhead, this reliably exhausts a 16KB stack and
results in early‑boot panics.  A 32KB stack eliminates these failures.

The new logic is:
    SPARC64:
        THREAD_SIZE = 4 * PAGE_SIZE (32KB)
        THREAD_SHIFT = PAGE_SHIFT + 2 (log₂(32KB))
        THREAD_SIZE_ORDER = 2 (4 contiguous pages)
    Non‑SPARC64 with PAGE_SHIFT == 13:
        Retains the existing 16KB stack behavior
    Fallback:
        Retains the existing 8KB stack behavior

Signed-off-by: Tony Rodriguez <unixpro1970@gmail.com>
---
 arch/sparc/include/asm/thread_info_64.h | 28 ++++++++++++-------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/arch/sparc/include/asm/thread_info_64.h b/arch/sparc/include/asm/thread_info_64.h
index c8a73dff27f8..6b12a2b66385 100644
--- a/arch/sparc/include/asm/thread_info_64.h
+++ b/arch/sparc/include/asm/thread_info_64.h
@@ -99,13 +99,20 @@ struct thread_info {
 #define FAULT_CODE_BLKCOMMIT	0x10	/* Use blk-commit ASI in copy_page */
 #define	FAULT_CODE_BAD_RA	0x20	/* Bad RA for sun4v		   */

-#if PAGE_SHIFT == 13
-#define THREAD_SIZE (2*PAGE_SIZE)
-#define THREAD_SHIFT (PAGE_SHIFT + 1)
-#else /* PAGE_SHIFT == 13 */
-#define THREAD_SIZE PAGE_SIZE
-#define THREAD_SHIFT PAGE_SHIFT
-#endif /* PAGE_SHIFT == 13 */
+/* thread information allocation */
+#ifdef CONFIG_SPARC64
+	#define THREAD_SIZE (4 * PAGE_SIZE)
+	#define THREAD_SHIFT (PAGE_SHIFT + 2)
+	#define THREAD_SIZE_ORDER 2
+#elif PAGE_SHIFT == 13
+	#define THREAD_SIZE (2 * PAGE_SIZE)
+	#define THREAD_SHIFT (PAGE_SHIFT + 1)
+	#define THREAD_SIZE_ORDER 1
+#else
+	#define THREAD_SIZE PAGE_SIZE
+	#define THREAD_SHIFT PAGE_SHIFT
+	#define THREAD_SIZE_ORDER 0
+#endif

 /*
  * macros/functions for gaining access to the thread information structure
@@ -127,13 +134,6 @@ register struct thread_info *current_thread_info_reg asm("g6");
 extern struct thread_info *current_thread_info(void);
 #endif

-/* thread information allocation */
-#if PAGE_SHIFT == 13
-#define THREAD_SIZE_ORDER	1
-#else /* PAGE_SHIFT == 13 */
-#define THREAD_SIZE_ORDER	0
-#endif /* PAGE_SHIFT == 13 */
-
 #define __thread_flag_byte_ptr(ti)	\
 	((unsigned char *)(&((ti)->flags)))
 #define __cur_thread_flag_byte_ptr	__thread_flag_byte_ptr(current_thread_info())
--
2.53.0