On Fri, Feb 20, 2009 at 07:09:51PM +0530, arun c wrote:
> PCI host machine (PPC cpu) writes commands to
> the PCI memory space of the (Coldfire CPU)
> target device. Target device takes the command
> and executes it.
>
> Target devices SDRAM is exposed over PCI to host.
> A circular buffer residing on target memory is used
> for command exchange.
>
> I should not allow host and target to play on the
> buffer simultaneously in order to avoid corruption.
>
> Does anybody know how to implement a lock
> suitable for this issue?
>
> or any lock less algorithm exists for communication
> over PCI?
I would have thought that a standard head and tail lockless queue would
be perfect for your application. Expressed in C:
struct queue {
unsigned head;
unsigned entries[QUEUE_SIZE];
unsigned tail;
}
int queue_size(struct queue __iomem *q)
{
int size = readl(&q->head) - readl(&q->tail);
if (size < 0)
size += QUEUE_SIZE;
return size;
}
int queue_empty(struct queue __iomem *q)
{
return readl(&q->head) == readl(&q->tail);
}
int queue_push(struct queue __iomem *q, unsigned item)
{
unsigned head = readl(&q->head) + 1;
if (head == readl(&q->tail))
return FAIL;
writel(&q->entries[head], item);
writel(&q->head, head);
}
Something like that anyway ... I obviously haven't tested or even
compiled it.
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
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