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Date: Sat, 29 Nov 2003 23:50:37 +0000
From: Joel Soete <soete.joel@tiscali.be>
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To: John David Anglin <dave@hiauly1.hia.nrc.ca>
Cc: randolph@tausq.org, parisc-linux@lists.parisc-linux.org
Subject: Re: [parisc-linux] [RFC] rewrite kernel spinlock code to work better
 with gcc
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John David Anglin wrote:
>>+/* Because kmalloc only guarantees 8-byte alignment for kmalloc'd data,
>>+   and GCC only guarantees 8-byte alignment for stack locals, we can't
>>+   be assured of 16-byte alignment for atomic lock data even if we
>>+   specify "__attribute ((aligned(16)))" in the type declaration.  So,
>>+   we use a struct containing an array of four ints for the atomic lock
>>+   type and dynamically select the 16-byte aligned int from the array
>>+   for the semaphore.  */
>>+#define __PA_LDCW_ALIGNMENT 16
>>+#define __ldcw_align(a) ({ \
>>+  unsigned long __ret = (unsigned long) a;                     		\
>>+  __ret = (__ret + __PA_LDCW_ALIGNMENT - 1) & ~(__PA_LDCW_ALIGNMENT - 1); \
>>+  (unsigned int *) __ret;                                               \
>>+})
> 
> 
> Change cast to "volatile unsigned int *".
> 
> 
>> typedef struct {
>>-	volatile unsigned int __attribute__((aligned(16))) lock;
>>+	volatile unsigned int lock[4];
>> } spinlock_t;
>> #endif
> 
> 
> Is the struct necessary?  For example,
> 
hmm i supposed that came from 2.4 struct:
typedef struct {
#ifdef CONFIG_PA20
	volatile unsigned int lock;
#else
	volatile unsigned int __attribute__((aligned(16))) lock;
#endif
#ifdef CONFIG_DEBUG_SPINLOCK
	volatile unsigned long owner_pc;
	volatile unsigned long owner_cpu;
#endif
} spinlock_t;

But I don't know yet if CONFIG_DEBUG_SPINLOCK is still foreseen for 2.6

Thanks,
	Joel