linux-kernel - Re: [PATCH v5 3/6] xen/arm: introduce xen_is_dma

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Message-ID: <1414142723.15687.24.camel@citrix.com>
Date:	Fri, 24 Oct 2014 10:25:23 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<david.vrabel@...rix.com>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <will.deacon@....com>
Subject: Re: [PATCH v5 3/6] xen/arm: introduce xen_is_dma_coherent

On Thu, 2014-10-23 at 18:27 +0100, Stefano Stabellini wrote:
> Introduce a utility function to check whether a device is dma coherent.
> The current implementation is suboptimal. Let's rework it later in
> common arch/arm code.
> 
> Use it to figure out whether we need to issue cache maintenance
> operations instead of checking on the existence of a particular dma_ops
> function for the device.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>

As well as refactoring this also changes the nature of the test, making
it tighter AFAICT. Perhaps it is the same because you happen to know
that arm_coherent_dma_ops is the only possible one which doesn't set the
hooks you were checking before.

Either way this should be mentioned in the commit log. With that done:

Acked-by: Ian Campbell <ian.campbell@...rix.com>

> 
> ---
> 
> Changes in v5:
> - introduce xen_is_dma_coherent as a xen specific function;
> - call xen_is_dma_coherent instead of is_dma_coherent.
> ---
>  arch/arm/include/asm/xen/page-coherent.h |    5 +++++
>  arch/arm/xen/mm32.c                      |    6 +++---
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/include/asm/xen/page-coherent.h b/arch/arm/include/asm/xen/page-coherent.h
> index e8275ea..6f0f882 100644
> --- a/arch/arm/include/asm/xen/page-coherent.h
> +++ b/arch/arm/include/asm/xen/page-coherent.h
> @@ -5,6 +5,11 @@
>  #include <linux/dma-attrs.h>
>  #include <linux/dma-mapping.h>
>  
> +static inline bool xen_is_dma_coherent(struct device *dev)
> +{
> +    return (__generic_dma_ops(dev) == &arm_coherent_dma_ops);
> +}
> + 
>  static inline void *xen_alloc_coherent_pages(struct device *hwdev, size_t size,
>  		dma_addr_t *dma_handle, gfp_t flags,
>  		struct dma_attrs *attrs)
> diff --git a/arch/arm/xen/mm32.c b/arch/arm/xen/mm32.c
> index 6153d61..6c0224e 100644
> --- a/arch/arm/xen/mm32.c
> +++ b/arch/arm/xen/mm32.c
> @@ -76,7 +76,7 @@ void xen_dma_unmap_page(struct device *hwdev, dma_addr_t handle,
>  		struct dma_attrs *attrs)
>  
>  {
> -	if (!__generic_dma_ops(hwdev)->unmap_page)
> +	if (xen_is_dma_coherent(hwdev))
>  		return;
>  	if (dma_get_attr(DMA_ATTR_SKIP_CPU_SYNC, attrs))
>  		return;
> @@ -87,7 +87,7 @@ void xen_dma_unmap_page(struct device *hwdev, dma_addr_t handle,
>  void xen_dma_sync_single_for_cpu(struct device *hwdev,
>  		dma_addr_t handle, size_t size, enum dma_data_direction dir)
>  {
> -	if (!__generic_dma_ops(hwdev)->sync_single_for_cpu)
> +	if (xen_is_dma_coherent(hwdev))
>  		return;
>  	__xen_dma_page_dev_to_cpu(hwdev, handle, size, dir);
>  }
> @@ -95,7 +95,7 @@ void xen_dma_sync_single_for_cpu(struct device *hwdev,
>  void xen_dma_sync_single_for_device(struct device *hwdev,
>  		dma_addr_t handle, size_t size, enum dma_data_direction dir)
>  {
> -	if (!__generic_dma_ops(hwdev)->sync_single_for_device)
> +	if (xen_is_dma_coherent(hwdev))
>  		return;
>  	__xen_dma_page_cpu_to_dev(hwdev, handle, size, dir);
>  }


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