linux-kernel - Re: ISP1760 driver crashes

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Date:	Wed, 19 Nov 2008 16:00:10 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	"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, Nov 19 2008, Alan Stern wrote:
> 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?

Sure, just use blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH), then you are
certain that you will always have a virtual mapping for the IO you
receive.

Or you can use the bio kmap/kunmap helpers to get such a mapping
temporarily if you wish. But if your pio condition is permanent, you may
as well just use bouncing.

-- 
Jens Axboe

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