[PATCH] Document Linux's memory barriers

Alan Cox alan at lxorguk.ukuu.org.uk
Wed Mar 8 06:33:41 EST 2006

On Maw, 2006-03-07 at 13:54 -0500, linux-os (Dick Johnson) wrote:
> On Tue, 7 Mar 2006, Alan Cox wrote:
> > 	writel(STOP_DMA, &foodev->ctrl);
> > 	free_dma_buffers(foodev);
> >
> > This leads to horrible disasters.
> This might be a good place to document:
>     dummy = readl(&foodev->ctrl);

Absolutely. And this falls outside of the memory barrier functions.
> Will flush all pending writes to the PCI bus and that:
>     (void) readl(&foodev->ctrl);
> ... won't because `gcc` may optimize it away. In fact, variable
> "dummy" should be global or `gcc` may make it go away as well.

If they were ordinary functions then maybe, but they are not so a simple
readl(&foodev->ctrl) will be sufficient and isn't optimised away.


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