linux-kernel - Re: ISP1760 driver crashes

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Date:	Wed, 19 Nov 2008 09:59:34 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Jens Axboe <axboe@...nel.dk>
cc:	"Hommel, Thomas (GE EntSol, Intelligent Platforms)" 
	<Thomas.Hommel@...anuc.com>, USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: ISP1760 driver crashes

On Wed, 19 Nov 2008, Sebastian Andrzej Siewior wrote:

> Hommel, Thomas (GE EntSol, Intelligent Platforms) wrote:
> 
> > I indeed have HIGHMEM enabled in my configuration.
> > I recompiled the kernel without HIGHMEM and it works. I don't think that
> > this a satisfying solution for a board with up to 2GB of RAM and
> > considerable amount of VMALLOC space, but at least this works.
> > If you have any more ideas how to circumvent this, please let me know.
> Sure, this is not a sollution but atleast now I know what happens:
> - The kernel allocates memory for transfer
> - the memory is highmem and not in kernel so the buffer is NULL
> - we don't have a dma-mask and therefore the dma address is 0
> - boom
> 
> The sollution would be probably to prevent the usb-storage core to 
> allocate memory from HIGHMEM.

usb-storage doesn't allocate the memory.  The memory is allocated by 
the block layer or the filesystem.

> Now I don't if there is a flag for something 
> like that and I am not using that. On the other hand this may be broken 
> for a long time and you are the first one which has that much memory with 
> no DMA-capable USB controller.

Jens, is there any way to tell the kernel that a device uses PIO and 
therefore its buffers shouldn't be allocated in high memory?  For 
example, shouldn't a NULL dma_mask do this?

If not, are there standard routines to set up bounce buffers for such 
devices?

Alan Stern

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