linux-kernel - Re: [PATCH 1/1] dma-mapping: to avoid exception when cpu

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Date:	Mon, 7 Mar 2016 20:22:00 +0800
From:	"Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Zefan Li <lizefan@...wei.com>, Xinwei Hu <huxinwei@...wei.com>,
	Tianhong Ding <dingtianhong@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>
Subject: Re: [PATCH 1/1] dma-mapping: to avoid exception when cpu_addr is NULL



On 2016/3/7 19:41, One Thousand Gnomes wrote:
> On Mon, 7 Mar 2016 17:21:25 +0800
> Zhen Lei <thunder.leizhen@...wei.com> wrote:
> 
>> Do this to keep consistent with kfree, which tolerate ptr is NULL.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> 
> This is inlined code so you are adding extra logic to every single
> instance of a call to the function. What is it's total effect on kernel
> size ?

This a simple if statement, I think it will only generates two instructions.
Maybe I need move it into function dma_free_attrs, as below:
if (!ops->free || !cpu_addr)
	return;

So that, it only generates one instruction. And dma_free_noncoherent can also be impacted.

Or I changed it to BUG_ON(!cpu_addr)?

Otherwise, I move it into ops->free, but that maybe more ARCHs.

> 
> Alan
> 
> .
>