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Date: Thu, 12 Jun 2008 22:04:05 +0300
From: Heikki Orsila <shdl@...alwe.fi>
To: David Altobelli <david.altobelli@...com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HP iLO driver
On Thu, Jun 12, 2008 at 12:23:08PM -0600, David Altobelli wrote:
> +struct fifo {
> + u64 nrents; /* user requested number of fifo entries */
> + u64 imask; /* mask to extract valid fifo index */
> + u64 merge; /* O/C bits to merge in during enqueue operation */
> + u64 reset; /* set to non-zero when the target device resets */
> + u8 pad_0[ILO_CACHE_SZ - (sizeof(u64) * 4)];
> +
> + u64 head;
> + u8 pad_1[ILO_CACHE_SZ - (sizeof(u64))];
> +
> + u64 tail;
> + u8 pad_2[ILO_CACHE_SZ - (sizeof(u64))];
> +
> + volatile u64 fifobar[1];
> +};
Why do you need a volatile? What you probably want is atomic ops.
Spinlocks will create memory barriers implicitly.
> +static int fifo_enqueue(struct ilo_hwinfo *hw, char *fifobar, int entry)
> +{
> + struct fifo *Q = FIFOBARTOHANDLE(fifobar);
> + int ret = 0;
> +
> + spin_lock(&hw->fifo_lock);
> + if (!(Q->fifobar[(Q->tail + 1) & Q->imask] & ENTRY_MASK_O)) {
> + Q->fifobar[Q->tail & Q->imask] |=
> + ((entry & ENTRY_MASK_NOSTATE) | Q->merge);
> + Q->tail += 1;
> + ret = 1;
> + }
> + spin_unlock(&hw->fifo_lock);
> +
> + return ret;
> +}
Is writing to Q->fifobar (u64 *) endian-safe?
--
Heikki Orsila
heikki.orsila@....fi
http://www.iki.fi/shd
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