From: Christoph Hellwig <hch@lst.de>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Christoph Hellwig <hch@lst.de>,
iommu@lists.linux-foundation.org,
Marek Szyprowski <m.szyprowski@samsung.com>,
Vladimir Murzin <vladimir.murzin@arm.com>,
Takashi Iwai <tiwai@suse.de>, Helge Deller <deller@gmx.de>,
Robin Murphy <robin.murphy@arm.com>,
Michal Simek <monstr@monstr.eu>,
linux-arm-kernel@lists.infradead.org,
linux-m68k@lists.linux-m68k.org, linux-parisc@vger.kernel.org,
linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org,
linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 7/8] parisc: don't set ARCH_NO_COHERENT_DMA_MMAP
Date: Mon, 19 Aug 2019 16:25:16 +0200 [thread overview]
Message-ID: <20190819142516.GA6366@lst.de> (raw)
In-Reply-To: <20190815105002.GA30805@lst.de>
Does my explanation from Thursday make sense or is it completely
off? Does the patch description need some update to be less
confusing to those used to different terminology?
On Thu, Aug 15, 2019 at 12:50:02PM +0200, Christoph Hellwig wrote:
> Except for the different naming scheme vs the code this matches my
> assumptions.
>
> In the code we have three cases (and a fourth EISA case mention in
> comments, but not actually implemented as far as I can tell):
>
> arch/parisc/kernel/pci-dma.c says in the top of file comments:
>
> ** AFAIK, all PA7100LC and PA7300LC platforms can use this code.
>
> and the handles two different case. for cpu_type == pcxl or pcxl2
> it maps the memory as uncached for dma_alloc_coherent, and for all
> other cpu types it fails the coherent allocations.
>
> In addition to that there are the ccio and sba iommu drivers, of which
> according to your above comment one is always present for pa8xxx.
>
> Which brings us back to this patch, which ensures that no cacheable
> memory is exported to userspace by removing ->mmap from ccio and sba.
> It then enabled dma_mmap_coherent for the pcxl or pcxl2 case that
> allocates uncached memory, which dma_mmap_coherent does not work
> because dma_alloc_coherent already failed for the !pcxl && !pcxl2
> and thus there is no memory to mmap.
>
> So if the description is too confusing please suggest a better
> one, I'm a little lost between all these code names and product
> names (arch/parisc/include/asm/dma-mapping.h uses yet another set).
---end quoted text---
next prev parent reply other threads:[~2019-08-19 14:25 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-08 15:59 remove default fallbacks in dma_map_ops v3 Christoph Hellwig
2019-08-08 15:59 ` [PATCH 1/8] dma-mapping: provide a better default ->get_required_mask Christoph Hellwig
2019-08-08 15:59 ` [PATCH 2/8] dma-mapping: move the dma_get_sgtable API comments from arm to common code Christoph Hellwig
2019-08-08 16:00 ` [PATCH 3/8] dma-mapping: explicitly wire up ->mmap and ->get_sgtable Christoph Hellwig
2019-08-08 16:00 ` [PATCH 4/8] dma-mapping: add a dma_can_mmap helper Christoph Hellwig
2019-08-08 16:00 ` [PATCH 5/8] ALSA: pcm: use dma_can_mmap() to check if a device supports dma_mmap_* Christoph Hellwig
2019-11-04 7:26 ` youling257
2019-08-08 16:00 ` [PATCH 6/8] arm-nommu: call dma_mmap_from_dev_coherent directly Christoph Hellwig
2019-08-09 9:35 ` Sergei Shtylyov
2019-08-08 16:00 ` [PATCH 7/8] parisc: don't set ARCH_NO_COHERENT_DMA_MMAP Christoph Hellwig
2019-08-15 7:36 ` Christoph Hellwig
2019-08-15 9:25 ` James Bottomley
2019-08-15 10:50 ` Christoph Hellwig
2019-08-19 14:25 ` Christoph Hellwig [this message]
2019-08-08 16:00 ` [PATCH 8/8] dma-mapping: remove CONFIG_ARCH_NO_COHERENT_DMA_MMAP Christoph Hellwig
2019-08-09 7:21 ` Geert Uytterhoeven
2019-08-29 15:38 ` remove default fallbacks in dma_map_ops v3 Christoph Hellwig
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