Re: [PATCH] arm64:swiotlb:Enable only when Input size through command line

[Robin Murphy]

Hi Konrad,

On 24/06/16 11:46, Konrad Rzeszutek Wilk wrote:
> On Fri, Jun 24, 2016 at 10:57:29AM +0800, Jisheng Zhang wrote:
>> Dear Konrad,
>>
>> On Thu, 23 Jun 2016 12:06:10 -0400 Konrad Rzeszutek Wilk wrote:
>>
>>> On June 23, 2016 10:30:34 AM EDT, Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
>>>> On Thu, Jun 23, 2016 at 05:43:40PM +0530, Manjeet Pawar wrote:  
>>>>> From: Rohit Thapliyal <r.thapliyal@xxxxxxxxxxx>
>>>>>
>>>>> swiotlb default size of 64M is too big as
>>>>> default value therefore it is made configurable
>>>>> through command line through swiotlb_size parameter.
>>>>> swiotlb allocation shall be done only when the
>>>>> swiotlb size is given through command line.
>>>>> Otherwise no swiotlb is allocated.  
>>>>
>>>> I already queued this patch:
>>>>
>>>> http://lkml.kernel.org/g/1465372426-4077-1-git-send-email-jszhang@xxxxxxxxxxx
>>>>
>>>> If you have any objections to it, please reply there.  
>>>
>>>
>>> I do (sorry about duplicate email, the other got rejected by mailing lists).
>>>
>>> Why not expand the swiotlb= parameter instead of introducing a new one?
>>
>> Do you mean pass "swiotlb=" for those platforms(most probably, arm64 with less
>> than 4GB DDR) which don't need swiotlb? I'm afraid this is not convenient, and
> 
> Why not just have a function that checks the amount of memory? x86 has
> that - if it finds that the machine has less than 4GB it will not setup
> SWIOTLB?
> 
>> users even don't notice swiotlb parameter. From another side, pass "swiotlb=0"
>> will make the swiotlb reserve 64MB instead, so how can we achieve zero reserved
>> memory for swiotlb through "swiotlb=" parameter?
> 
> Obviously make the function understand that 0 is to turn it off.
>>
>> PS: my patch didn't introduce new boot parameter.
> 
> swiotlb_sz ?

Note that Jisheng's patch is the one Catalin linked to, *not* this one,
and more or less does exactly what you describe.

Robin.

>>
>> I'm not sure I got your meaning, so could you please comment my patch
>> directly?
>>
>> Thanks,
>> Jisheng
>>
>>>
>>> Also, why not use the swiotlb by itself? That does the job as well?
>>>
>>>
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>>
> 
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