From: Thomas Bogendoerfer <tbogendoerfer@suse.de>
To: Joshua Kinard <kumba@gentoo.org>
Cc: Christoph Hellwig <hch@infradead.org>,
Ralf Baechle <ralf@linux-mips.org>,
Paul Burton <paul.burton@mips.com>,
James Hogan <jhogan@kernel.org>,
linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] MIPS: add support for SGI Octane (IP30)
Date: Mon, 14 Oct 2019 13:34:08 +0200 [thread overview]
Message-ID: <20191014133408.24fb17711d942effc92e27ee@suse.de> (raw)
In-Reply-To: <5c6ab720-218a-14aa-9112-a12b88b63bc2@gentoo.org>
On Fri, 11 Oct 2019 20:33:43 -0400
Joshua Kinard <kumba@gentoo.org> wrote:
> http://bxr.su/OpenBSD/sys/arch/sgi/sgi/ip30_machdep.c
>
> 144 /*
> 145 * Register DMA-reachable memory constraints.
> 146 * The xbridge(4) is limited to a 31-bit region (its IOMMU features
> 147 * are too restricted to be of use).
> 148 */
> 149 dma_constraint.ucr_low = 0;
> 150 dma_constraint.ucr_high = (1UL << 31) - 1;
>
> I never figured out how in Linux one does something equivalent. I knew it
> needed to be done in the older dma-coherence.h file, and now in the newer
> __phys_to_dma() function here. This is, if memory recalls correctly,
> because >2GB RAM in Octane causes issues w/ BRIDGE DMA access.
32bit DMA is always limited to 2GB address range by bridge. Right now we
our code doesn't support 32bit DMA access at all, because it was not really
usefull for IP27. With IP30 it's probably more usefull, but my current focus
is getting basic IP30 support merged and improve it from there. And as this
is a bridge limititation everything can still be placed in pci-xtalk-bridge.c
Thomas.
--
SUSE Software Solutions Germany GmbH
HRB 247165 (AG München)
Geschäftsführer: Felix Imendörffer
prev parent reply other threads:[~2019-10-14 11:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 15:59 [PATCH] MIPS: add support for SGI Octane (IP30) Thomas Bogendoerfer
2019-10-09 18:43 ` Christoph Hellwig
2019-10-10 13:01 ` Thomas Bogendoerfer
2019-10-10 13:53 ` Christoph Hellwig
2019-10-10 14:48 ` Thomas Bogendoerfer
2019-10-10 14:58 ` Carlo Pisani
2019-10-12 0:33 ` Joshua Kinard
2019-10-14 11:34 ` Thomas Bogendoerfer [this message]
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