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

[Konrad Rzeszutek Wilk]

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 ?

> 
> 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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>