linux-kernel - Re: [PATCH v2] staging: ion: Add a default struct device for cma heap

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Date:	Thu, 6 Aug 2015 21:54:04 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Feng Tang <feng.tang@...el.com>
Cc:	John Stultz <john.stultz@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] staging: ion: Add a default struct device for cma heap

On Fri, Aug 07, 2015 at 11:50:13AM +0800, 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.
> 
> This patch adds one default device for each 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 recently,
> this patch also adds 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..11336df 100644
> --- a/drivers/staging/android/ion/ion.h
> +++ b/drivers/staging/android/ion/ion.h
> @@ -44,6 +44,9 @@ struct ion_buffer;
>   * @base:	base address of heap in physical memory if applicable
>   * @size:	size of the heap in bytes if applicable
>   * @align:	required alignment in physical memory if applicable
> + * @cma:	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
>   * @priv:	private info passed from the board file
>   *
>   * Provided by the board file.
> @@ -55,6 +58,7 @@ struct ion_platform_heap {
>  	ion_phys_addr_t base;
>  	size_t size;
>  	ion_phys_addr_t align;
> +	struct cma *cma;
>  	void *priv;
>  };
>  
> diff --git a/drivers/staging/android/ion/ion_cma_heap.c b/drivers/staging/android/ion/ion_cma_heap.c
> index f4211f1..27f218a 100644
> --- a/drivers/staging/android/ion/ion_cma_heap.c
> +++ b/drivers/staging/android/ion/ion_cma_heap.c
> @@ -29,6 +29,7 @@
>  struct ion_cma_heap {
>  	struct ion_heap heap;
>  	struct device *dev;
> +	struct device default_dma_dev;

Why do we have 2 struct devices here?

>  };
>  
>  #define to_cma_heap(x) container_of(x, struct ion_cma_heap, heap)
> @@ -180,9 +181,22 @@ struct ion_heap *ion_cma_heap_create(struct ion_platform_heap *data)
>  		return ERR_PTR(-ENOMEM);
>  
>  	cma_heap->heap.ops = &ion_cma_ops;
> -	/* get device from private heaps data, later it will be
> -	 * used to make the link with reserved CMA memory */
> -	cma_heap->dev = data->priv;
> +
> +	/*
> +	 * 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;

That's not good, it's not initialized, or if it is, what's the lifetime
rules for it now?

Why are you needing an extra struct device now?

this seems odd.

greg k-h
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