From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: "Prakash, Sathya" <Sathya.Prakash@lsi.com>, linux-scsi@vger.kernel.org
Subject: Re: Query regarding modifying the DMA Mask based on the available memory in the system
Date: Thu, 17 Apr 2008 10:03:41 -0500 [thread overview]
Message-ID: <1208444622.3150.10.camel@localhost.localdomain> (raw)
In-Reply-To: <87iqygk0bu.fsf@basil.nowhere.org>
On Thu, 2008-04-17 at 16:44 +0200, Andi Kleen wrote:
> >
> > For drivers that can alter their descriptor types, we have this
> > function:
> >
> > dma_get_required_mask()
>
> Are you sure we have it? It seems to be in drivers/base/platform.c
> conditional on ARCH_HAS_DMA_GET_REQUIRED_MASK, but according to my
> grep no architecture ever sets that flag.
Yes ... positive. That's the default and correct implementation based
on the largest addressable physical memory.
> I don't think it would be very hard to implement on x86 at least,
> mind you. Just nobody seems to have done it so far.
Really, only machines with IOMMUs that want to restrict this need
implement it. Current safety is predicated on the assumption that no
architectures with IOMMUs never return bus physical addresses above
memory physical. If that's not true, then they *have* to implement
this. For all others its an optimisation to return a more restricted
range.
James
next prev parent reply other threads:[~2008-04-17 15:03 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-17 8:40 Query regarding modifying the DMA Mask based on the available memory in the system Prakash, Sathya
2008-04-17 8:43 ` David Miller
2008-04-17 10:06 ` Andi Kleen
2008-04-17 14:18 ` James Bottomley
2008-04-17 14:44 ` Andi Kleen
2008-04-17 15:03 ` James Bottomley [this message]
2008-04-17 15:06 ` Andi Kleen
2008-04-17 15:36 ` James Bottomley
2008-04-17 16:10 ` Andi Kleen
-- strict thread matches above, loose matches on Subject: below --
2008-04-17 17:36 Prakash, Sathya
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