linux-kernel - Re: [PATCH] staging: ion: Add a default struct device for cma heap

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Date:	Thu, 6 Aug 2015 09:57:41 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Feng Tang <feng.tang@...el.com>
Cc:	Michal Nazarewicz <mina86@...a86.com>,
	John Stultz <john.stultz@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: ion: Add a default struct device for cma heap

On Thu, Aug 06, 2015 at 11:25:15PM +0800, Feng Tang wrote:
> Hi Michal,
> 
> Thanks for the review!
> 
> On Thu, Aug 06, 2015 at 01:40:28PM +0200, Michal Nazarewicz wrote:
> > On Thu, Aug 06 2015, Feng Tang wrote:
> > > When trying to use several cma heaps on our platforms,
> > > we met a memory issue due to that the several cma_heaps
> > > are sharing the same "struct device *".
> > >
> > > As in current code base, the normal cma heap creating
> > > process is, one platform device is created during boot,
> > > and it will sequentially create cma heaps (usually passing
> > > its own struct device * as a parameter)
> > >
> > > For the multiple cma heaps case, there will be one "struct
> > > cma" created for each cma heap, and this "struct cma *" is
> > > saved in dev->cma_area. So the single platform device can't
> > > meet the requirement here.
> > >
> > > So this patch add one default device for a cma heap to avoid
> > > sharing the same "struct device", thus fix the issue. And it
> > > doesn't break existing code by only using that default device
> > > when no "struct device *" is passed in.
> > >
> > > Also, since the cma framework has been cleaned up, this patch
> > > also add a platform data member to pass the "struct cma*" to
> > > ion_cma_heap_create().
> > >
> > > Signed-off-by: Feng Tang <feng.tang@...el.com>
> > 
> > >From CMA’s point of view:
> > 
> > Acked-by: Michal Nazarewicz <mina86@...a86.com>
> > 
> > > ---
> > >  drivers/staging/android/ion/ion.h          |    4 ++++
> > >  drivers/staging/android/ion/ion_cma_heap.c |   20 +++++++++++++++++---
> > >  2 files changed, 21 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/staging/android/ion/ion.h b/drivers/staging/android/ion/ion.h
> > > index 443db84..e9af17e 100644
> > > --- a/drivers/staging/android/ion/ion.h
> > > +++ b/drivers/staging/android/ion/ion.h
> > > @@ -45,6 +45,9 @@ struct ion_buffer;
> > >   * @size:	size of the heap in bytes if applicable
> > >   * @align:	required alignment in physical memory if applicable
> > >   * @priv:	private info passed from the board file
> > > + * @priv2:	when creating CMA heap, platform device should better also
> > > + *		pass the "struct cma *" info, so that the cma buffer request
> > > + *		know where to go for the buffer
> > >   *
> > >   * Provided by the board file.
> > >   */
> > > @@ -56,6 +59,7 @@ struct ion_platform_heap {
> > >  	size_t size;
> > >  	ion_phys_addr_t align;
> > >  	void *priv;
> > > +	void *priv2;
> > 
> > Why are those void pointers anyway? Perhaps just make them struct device
> > *dev and struct cma *cma? Especially since priv2 is a bit awkward name.
>  
> My initial thought is the same, but as there are several other kinds of ion
> heaps which are also using this structure for their own
> ion_xxx_heap_create(struct ion_platform_heap *), I gave up using the
> explicit "struct cma *", in case other kinds of heaps may need to use
> this additional priv2 in future

No, just make it a struct cma *, as that's what it is.  Having multiple
void * is a sign of a very crazy interface.

thanks,

greg k-h
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