Re: [patch] 2.3.39: Don't use bounce buffer when not needed (parport)

[Matthew Wilcox]

On Wed, Jan 12, 2000 at 12:56:27PM +0000, Tim Waugh wrote:
> This patch from Bert De Jonghe avoids a memcpy when it isn't needed.  
> Since parport_pc.c is used by several architectures, should this be
> protected with #ifdef __i386__?  I'm not sure if architectures like Sparc
> or Alpha have the same DMA limitation.

[...]

> +	/* above 16 MB we use a bounce buffer as ISA-DMA is not possible */
> +	if ((dma_addr + length) >= 0x1000000L) {  
> +		maxlen   = PAGE_SIZE;          /* sizeof(priv->dma_buf) */
> +		dma_addr = virt_to_bus((volatile char *) priv->dma_buf);
> +	}
> +

You can make this arch-independent by using ISA_DMA_THRESHOLD which is
defined in <asm/scatterlist.h>.  This probably isn't a good place to keep
this definition, but it is there.