linux-kernel - RE: [PATCH v5] modify the IO_TLB_SEGSIZE and IO_TLB_DEFAULT_SIZE configurable as flexible requirement about SW-IOMMU.

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Message-Id: <54F8247B02000078000667AF@mail.emea.novell.com>
Date:	Thu, 05 Mar 2015 08:40:11 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Xiaoming Wang" <xiaoming.wang@...el.com>
Cc:	"Liu@...rp2030.oracle.com" <Liu@...rp2030.oracle.com>,
	"Zhang@...rp2030.oracle.com" <Zhang@...rp2030.oracle.com>,
	"chris@...is-wilson.co.uk" <chris@...is-wilson.co.uk>,
	"david.vrabel@...rix.com" <david.vrabel@...rix.com>,
	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
	"linux@...izon.com" <linux@...izon.com>,
	"Chuansheng Liu" <chuansheng.liu@...el.com>,
	"Dongxing Zhang" <dongxing.zhang@...el.com>,
	"takahiro.akashi@...aro.org" <takahiro.akashi@...aro.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	"d.kasatkin@...sung.com" <d.kasatkin@...sung.com>,
	"pebolle@...cali.nl" <pebolle@...cali.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5] modify the IO_TLB_SEGSIZE and
 IO_TLB_DEFAULT_SIZE configurable as flexible requirement about
 SW-IOMMU.

>>> On 05.03.15 at 04:53, <xiaoming.wang@...el.com> wrote:
>> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@...cle.com]
>> Sent: Thursday, March 5, 2015 3:43 AM
>> On Tue, Mar 03, 2015 at 04:11:09PM +0800, Wang Xiaoming wrote:
>> > @@ -101,13 +119,32 @@ setup_io_tlb_npages(char *str)  {
>> >  	if (isdigit(*str)) {
>> >  		io_tlb_nslabs = simple_strtoul(str, &str, 0);
>> > -		/* avoid tail segment of size < IO_TLB_SEGSIZE */
>> > -		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
>> >  	}
>> >  	if (*str == ',')
>> >  		++str;
>> > -	if (!strcmp(str, "force"))
>> > +	if (!strncmp(str, "force", 5)) {
>> >  		swiotlb_force = 1;
>> > +		str += 5;
>> > +	}
>> 
>> So the format is now:
>> 
>> 	Format: { <int> | force | <int> | <int>}
>> 
>> which means I can do
>> 	32,22323,force
>> 
>> Or
>> 	force,32
>> 
>> Or
>> 	32,force
>> 
> If I use Format: { <int>,force,<int>,<int>}
> 32,22323,force can't acceptable.
> There are three  <int>  here, if there are out of order, that will cause 
> confuse.
> Only 	32,force,32323
> Or	32,,32323,2322
> Or	,,323222,3232
> Are available.

You need to make sure that all previously valid variants are still
usable, i.e. force alone, a number alone, force,<number> and
<number>,force. How many variants you want to support with
your additions is mostly up to you; I'd recommend permitting force
in any position.

Jan

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