linux-kernel - Re: [PATCH v4 6/7] xen/arm/arm64: introduce xen_arch_need

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Date:	Tue, 14 Oct 2014 17:12:12 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	<xen-devel@...ts.xensource.com>, <Ian.Campbell@...rix.com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 6/7] xen/arm/arm64: introduce xen_arch_need_swiotlb

On 14/10/14 17:03, Konrad Rzeszutek Wilk wrote:
> On Fri, Oct 10, 2014 at 12:51:47PM +0100, Stefano Stabellini wrote:
>> Introduce an arch specific function to find out whether a particular dma
>> mapping operation needs to bounce on the swiotlb buffer.
>>
>> On ARM and ARM64, if the page involved is a foreign page and the device
>> is not coherent, we need to bounce because at unmap time we cannot
>> execute any required cache maintenance operations (we don't know how to
>> find the pfn from the mfn).
...
>> --- a/arch/x86/include/asm/xen/page.h
>> +++ b/arch/x86/include/asm/xen/page.h
>> @@ -236,4 +236,11 @@ void make_lowmem_page_readwrite(void *vaddr);
>>  #define xen_remap(cookie, size) ioremap((cookie), (size));
>>  #define xen_unmap(cookie) iounmap((cookie))
>>  
>> +static inline bool xen_arch_need_swiotlb(struct device *dev,
>> +		                                 unsigned long pfn,
>> +										 unsigned long mfn)
>> +{
>> +	return false;
>> +}
> 
> Why not make this an macro?

Because macros are evil and inline functions are preferred.

David
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