linux-kernel - Re: staging: Unwritten function for ion_carveout

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Date:	Wed, 23 Jul 2014 13:10:29 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Nick Krause <xerofoify@...il.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	John Stultz <john.stultz@...aro.org>,
	Rebecca Zavin <rebecca@...roid.com>,
	Laura Abbott <lauraa@...eaurora.org>, gioh.kim@....com,
	benjamin.gaignard@...aro.org,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: staging: Unwritten function for ion_carveout_heap.c

On Wed, Jul 23, 2014 at 1:04 PM, Nick Krause <xerofoify@...il.com> wrote:
> Hey Greg and others.
> Sorry for another email but it seems the function,
> ion_carveout_heap_unmap_dma is
> just returning and not doing anything useful. Furthermore I am new so
> I don't known how
> to write this function but this may  be causing  some rather  serious
> bugs as if the dma heap
> is not unmaped and we  call this function a lot this will make the
> kernel not able to handle dma requests
> for this driver and other drivers that need this and in turn lead to
> a oops or even a kernel panic due to leaked
> dma allocated memory. I would recommend writing this function or
> helping me write it in
> other to avoid some rather serious bugs without a proper dma unmapping
> function for this driver  :).
> Nick

Look at ion_carveout_heap_map_dma - it doesn't do anything, it just
returns a pre-existing virtual address.  That means there is nothing
to do in unmap.

map_dma is actually a bit of a misnomer here, as the actual mapping is
done in ion_map_dma_buf.  All ion_carveout_heap_map_dma does is return
the sg table for ion_map_dma_buf to pass to dma_map_sg.
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