From: Christoph Hellwig <hch@lst.de>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: linux-xtensa@linux-xtensa.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, iommu@lists.linux-foundation.org,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/4] vmalloc: lift the arm flag for coherent mappings to common code
Date: Fri, 30 Aug 2019 16:59:35 +0200 [thread overview]
Message-ID: <20190830145935.GA19838@lst.de> (raw)
In-Reply-To: <20190830092918.GV13294@shell.armlinux.org.uk>
On Fri, Aug 30, 2019 at 10:29:18AM +0100, Russell King - ARM Linux admin wrote:
> On Fri, Aug 30, 2019 at 08:29:21AM +0200, Christoph Hellwig wrote:
> > The arm architecture had a VM_ARM_DMA_CONSISTENT flag to mark DMA
> > coherent remapping for a while. Lift this flag to common code so
> > that we can use it generically. We also check it in the only place
> > VM_USERMAP is directly check so that we can entirely replace that
> > flag as well (although I'm not even sure why we'd want to allow
> > remapping DMA appings, but I'd rather not change behavior).
>
> Good, because if you did change that behaviour, you'd break almost
> every ARM framebuffer and cripple ARM audio drivers.
How would that break them? All the usual video and audio drivers that
use dma_alloc_* then use dma_mmap_* which never end up in the only place
that actually checks VM_USERMAP (remap_vmalloc_range_partial) as they
end up in the dma_map_ops mmap methods which contain what is effecitvely
open coded versions of that routine. There are very few callers of
remap_vmalloc_range_partial / remap_vmalloc_range, and while a few of
those actually are in media drivers and the virtual frame buffer video
driver, none of these seems to be called on dma memory (which would
be a layering violation anyway).
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: linux-xtensa@linux-xtensa.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, iommu@lists.linux-foundation.org,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/4] vmalloc: lift the arm flag for coherent mappings to common code
Date: Fri, 30 Aug 2019 16:59:35 +0200 [thread overview]
Message-ID: <20190830145935.GA19838@lst.de> (raw)
In-Reply-To: <20190830092918.GV13294@shell.armlinux.org.uk>
On Fri, Aug 30, 2019 at 10:29:18AM +0100, Russell King - ARM Linux admin wrote:
> On Fri, Aug 30, 2019 at 08:29:21AM +0200, Christoph Hellwig wrote:
> > The arm architecture had a VM_ARM_DMA_CONSISTENT flag to mark DMA
> > coherent remapping for a while. Lift this flag to common code so
> > that we can use it generically. We also check it in the only place
> > VM_USERMAP is directly check so that we can entirely replace that
> > flag as well (although I'm not even sure why we'd want to allow
> > remapping DMA appings, but I'd rather not change behavior).
>
> Good, because if you did change that behaviour, you'd break almost
> every ARM framebuffer and cripple ARM audio drivers.
How would that break them? All the usual video and audio drivers that
use dma_alloc_* then use dma_mmap_* which never end up in the only place
that actually checks VM_USERMAP (remap_vmalloc_range_partial) as they
end up in the dma_map_ops mmap methods which contain what is effecitvely
open coded versions of that routine. There are very few callers of
remap_vmalloc_range_partial / remap_vmalloc_range, and while a few of
those actually are in media drivers and the virtual frame buffer video
driver, none of these seems to be called on dma memory (which would
be a layering violation anyway).
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>,
iommu@lists.linux-foundation.org,
Robin Murphy <robin.murphy@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-xtensa@linux-xtensa.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] vmalloc: lift the arm flag for coherent mappings to common code
Date: Fri, 30 Aug 2019 16:59:35 +0200 [thread overview]
Message-ID: <20190830145935.GA19838@lst.de> (raw)
In-Reply-To: <20190830092918.GV13294@shell.armlinux.org.uk>
On Fri, Aug 30, 2019 at 10:29:18AM +0100, Russell King - ARM Linux admin wrote:
> On Fri, Aug 30, 2019 at 08:29:21AM +0200, Christoph Hellwig wrote:
> > The arm architecture had a VM_ARM_DMA_CONSISTENT flag to mark DMA
> > coherent remapping for a while. Lift this flag to common code so
> > that we can use it generically. We also check it in the only place
> > VM_USERMAP is directly check so that we can entirely replace that
> > flag as well (although I'm not even sure why we'd want to allow
> > remapping DMA appings, but I'd rather not change behavior).
>
> Good, because if you did change that behaviour, you'd break almost
> every ARM framebuffer and cripple ARM audio drivers.
How would that break them? All the usual video and audio drivers that
use dma_alloc_* then use dma_mmap_* which never end up in the only place
that actually checks VM_USERMAP (remap_vmalloc_range_partial) as they
end up in the dma_map_ops mmap methods which contain what is effecitvely
open coded versions of that routine. There are very few callers of
remap_vmalloc_range_partial / remap_vmalloc_range, and while a few of
those actually are in media drivers and the virtual frame buffer video
driver, none of these seems to be called on dma memory (which would
be a layering violation anyway).
next prev parent reply other threads:[~2019-08-30 15:01 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-30 6:29 cleanup vmap usage in the dma-mapping layer Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-08-30 6:29 ` [PATCH 1/4] vmalloc: lift the arm flag for coherent mappings to common code Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-08-30 9:29 ` Russell King - ARM Linux admin
2019-08-30 9:29 ` Russell King - ARM Linux admin
2019-08-30 9:29 ` Russell King - ARM Linux admin
2019-08-30 14:59 ` Christoph Hellwig [this message]
2019-08-30 14:59 ` Christoph Hellwig
2019-08-30 14:59 ` Christoph Hellwig
2019-08-30 6:29 ` [PATCH 2/4] dma-mapping: always use VM_DMA_COHERENT for generic DMA remap Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-08-30 6:29 ` [PATCH 3/4] dma-mapping: introduce a dma_common_find_pages helper Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-10-02 12:05 ` Geert Uytterhoeven
2019-10-02 12:05 ` Geert Uytterhoeven
2019-10-02 12:05 ` Geert Uytterhoeven
2019-10-02 16:45 ` Robin Murphy
2019-10-02 16:45 ` Robin Murphy
2019-10-02 16:45 ` Robin Murphy
2019-10-06 18:45 ` Christoph Hellwig
2019-10-06 18:45 ` Christoph Hellwig
2019-10-06 18:45 ` Christoph Hellwig
2019-10-07 7:35 ` Geert Uytterhoeven
2019-10-07 7:35 ` Geert Uytterhoeven
2019-10-07 7:35 ` Geert Uytterhoeven
2019-08-30 6:29 ` [PATCH 4/4] arm: remove wrappers for the generic dma remap helpers Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
2019-08-30 6:29 ` Christoph Hellwig
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