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

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Date:	Thu, 6 Aug 2015 23:25:15 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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

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

> > +	 * data->priv for cma heap is currently supposed to point
> > +	 * to a "struct device *"
> > +	 */
> > +	if (data->priv) {
> > +		cma_heap->dev = data->priv;
> > +	} else {
> > +		cma_heap->dev = &cma_heap->default_dma_dev;
> > +		cma_heap->dev->coherent_dma_mask = DMA_BIT_MASK(32);
> > +		cma_heap->dev->dma_mask = &dev->coherent_dma_mask;
> > +	}
> > +
> > +	/* data->priv2 contains a pointer to struct cma */
> > +	dev_set_cma_area(cma_heap->dev, data->priv2);
> 
> Perhaps:
> 
> +	if (data->priv2)
> +		dev_set_cma_area(cma_heap->dev, data->priv2);

Yes, this looks more logical, even though the cma_heap structure is
kzalloced.

Thanks,
Feng
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