linux-kernel - Re: [Xen-devel] [PATCH v4] modify the IO_TLB_SEGSIZE and IO_TLB_DEFAULT_SIZE configurable as flexible requirement about SW-IOMMU.

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Date:	Tue, 17 Feb 2015 10:08:48 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Wang Xiaoming" <xiaoming.wang@...el.com>
Cc:	<chris@...is-wilson.co.uk>, <david.vrabel@...rix.com>,
	<lauraa@...eaurora.org>, <heiko.carstens@...ibm.com>,
	<linux@...izon.com>, "Chuansheng Liu" <chuansheng.liu@...el.com>,
	"Zhang Dongxing" <dongxing.zhang@...el.com>,
	<takahiro.akashi@...aro.org>, <akpm@...ux-foundation.org>,
	<linux-mips@...ux-mips.org>, <ralf@...ux-mips.org>,
	<xen-devel@...ts.xenproject.org>, <boris.ostrovsky@...cle.com>,
	<konrad.wilk@...cle.com>, <d.kasatkin@...sung.com>,
	<pebolle@...cali.nl>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH v4] modify the IO_TLB_SEGSIZE and
 IO_TLB_DEFAULT_SIZE configurable as flexible requirement about
 SW-IOMMU.

>>> On 17.02.15 at 07:51, <xiaoming.wang@...el.com> wrote:
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -3438,10 +3438,12 @@ bytes respectively. Such letter suffixes can also be 
> entirely omitted.
>  			it if 0 is given (See Documentation/cgroups/memory.txt)
>  
>  	swiotlb=	[ARM,IA-64,PPC,MIPS,X86]
> -			Format: { <int> | force }
> +			Format: { <int> | force | <int> | <int>}
>  			<int> -- Number of I/O TLB slabs
>  			force -- force using of bounce buffers even if they
>  			         wouldn't be automatically used by the kernel
> +			<int> -- Maximum allowable number of contiguous slabs to map
> +			<int> -- The size of SW-MMU mapped.

This makes no sense - the new numbers added aren't position
independent (nor were the previous <int> and "force").

Also you are (supposedly) removing all uses of
IO_TLB_DEFAULT_SIZE, yet you don't seem to remove the
definition itself.

Finally - are arbitrary numbers really okay for the newly added
command line options? I.e. shouldn't you add some checking of
their validity?

Jan

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