Re: Scatter-Gather buffer allocation before running on HDSP-MADI ?

[Takashi Iwai <tiwai@suse.de>]

At Fri, 10 Oct 2003 11:03:36 +0200 (CEST),
ritsch@iem.at wrote:
> 
> Hello,
> 
> 
> the hdsp-madi card with the hdspm driver seems to work now.
> so I want do a clean out of the code:
> 
> I asking how should I do this:
> 
> > > at least I have to allocate one page more = 4194304+4096, to get no
> > > Segmentation fault, but that could be the hardware too, since hdsp
> > > also needs one page more ?
> > 
> > the SG-buffer allocation size is aligned (round up) to PAGE_SIZE.
> > (note that PAGE_SIZE is not always 4K byte on other architectures.)
> > 
> 
> Ok on my i386 architecture I have 4k pages and
> the rme card needs  4k buffers.
> 
> So how to code this that it works on all architectures getting
> a SG Buf with 4k buffers.
> 
> Do I have to do something by doing preallocation ?

on linux, the least page size is 4K byte (so far, all architectures
are so).  thus, simply do a loop like

	offset = 0; /* bytes */
	while (offset < total_size) {
		dma_addr_t addr = snd_sgbuf_get_addr(sgbuf, offset);
		map_this_addr_to_my_hw_table(addr);
		offset += 4096; /* 4k */
	}


Takashi


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