From: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: hancockrwd@gmail.com, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [RFC PATCH] fix problems with NETIF_F_HIGHDMA in networking drivers
Date: Sat, 27 Feb 2010 12:59:31 +0100 [thread overview]
Message-ID: <201002271259.31596.bzolnier@gmail.com> (raw)
In-Reply-To: <20100227.015350.71138134.davem@davemloft.net>
On Saturday 27 February 2010 10:53:50 am David Miller wrote:
> From: Robert Hancock <hancockrwd@gmail.com>
> Date: Fri, 26 Feb 2010 21:08:04 -0600
>
> > That seems like a reasonable approach to me. Only question is how to
> > implement the check for DMA_64BIT. Can we just check page_to_phys on
> > each of the pages in the skb to see if it's > 0xffffffff ? Are there
> > any architectures where it's more complicated than that?
>
> On almost every platform it's "more complicated than that".
Mildly speaking, I see the real problem now and it is much higher in
the software stack than networking..
> This is the whole issue. What matters is the final DMA address and
> since we have IOMMUs and the like, it is absolutely not tenable to
> solve this by checking physical address attributes.
What's more we may not have IOMMU in place which creates really interesting
scenarios for HIGHMEM=y and results in all kind of wonderful band-aids in
particular device drivers.
Having IOMMU (even if it is only a software one, i.e. this would mean
swiotlb for x86-32/highmem) always in place would simplify things greatly..
--
Bartlomiej Zolnierkiewicz
next prev parent reply other threads:[~2010-02-27 12:00 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-23 2:45 [RFC PATCH] fix problems with NETIF_F_HIGHDMA in networking drivers Robert Hancock
2010-02-26 9:36 ` David Miller
[not found] ` <20100226.013637.255461265.davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
2010-02-26 14:46 ` Robert Hancock
2010-02-26 15:25 ` Bartlomiej Zolnierkiewicz
2010-02-27 3:08 ` Robert Hancock
2010-02-27 9:53 ` David Miller
2010-02-27 11:59 ` Bartlomiej Zolnierkiewicz [this message]
2010-02-27 12:05 ` David Miller
2010-02-27 18:15 ` Robert Hancock
2010-02-27 18:38 ` FUJITA Tomonori
[not found] ` <20100228033706G.fujita.tomonori-Zyj7fXuS5i5L9jVzuh4AOg@public.gmane.org>
2010-02-28 8:16 ` David Miller
2010-03-01 16:34 ` Was: Re: [RFC PATCH] fix problems with NETIF_F_HIGHDMA in networking, Now: SWIOTLB dynamic allocation Konrad Rzeszutek Wilk
2010-03-01 21:12 ` Robert Hancock
2010-03-02 4:40 ` FUJITA Tomonori
2010-03-02 4:40 ` FUJITA Tomonori
2010-02-27 17:59 ` [RFC PATCH] fix problems with NETIF_F_HIGHDMA in networking drivers Robert Hancock
[not found] ` <51f3faa71002270959o4d1435e3xf67185fccaf50b18-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-02-27 18:38 ` FUJITA Tomonori
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