netdev - Re: [PATCH] wireless: iwlwifi - add dma_mapping

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Date:	Mon, 05 Nov 2012 09:44:57 -0700
From:	Shuah Khan <shuah.khan@...com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	wey-yi.w.guy@...el.com, linville@...driver.com,
	ilw@...ux.intel.com, emmanuel.grumbach@...el.com,
	donald.h.fry@...el.com, linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	shuahkhan@...il.com
Subject: Re: [PATCH] wireless: iwlwifi - add dma_mapping_error() checks to
 avoid warnings

On Mon, 2012-11-05 at 17:29 +0100, Johannes Berg wrote:
> On Mon, 2012-11-05 at 09:26 -0700, Shuah Khan wrote:
> 
> > > Thanks for the report. Since I think doing BUG_ON() in such a scenario
> > > is a really bad idea, I've applied a different patch with your
> > > Reported-by.
> > 
> > Yeah. I wasn't sure about BUS() either. Did you notice the other cases
> > of BUG_ON() in this path in iwl_rx_allocate()? I would think those need
> > fixing as well.
> > 
> >               rxb->page_dma =
> >                         dma_map_page(trans->dev, page, 0,
> >                                      PAGE_SIZE <<
> > trans_pcie->rx_page_order,
> >                                      DMA_FROM_DEVICE);
> >                 /* dma address must be no more than 36 bits */
> >                 BUG_ON(rxb->page_dma & ~DMA_BIT_MASK(36));
> >                 /* and also 256 byte aligned! */
> >                 BUG_ON(rxb->page_dma & DMA_BIT_MASK(8));
> 
> Well, yes, we could convert them, but we can leave them as they are
> because these are assertions that the DMA mapping API guarantees. If
> this breaks, it's a bug in the DMA mapping code.
> 
> In contrast, if it fails to map, it's not a bug in the code, it's just
> running out of memory or IO space or whatever.

Right.
> 
> > Could you please send me commitID for the patch you did. I am interested
> > in seeing the failure handling in your patch?
> 
> It's here:
> http://git.kernel.org/?p=linux/kernel/git/iwlwifi/iwlwifi-fixes.git;a=commit;h=7c34158231b2eda8dcbd297be2bb1559e69cb433
> 


Thanks. 


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