From: m.szyprowski@samsung•com (Marek Szyprowski)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC PATCH 0/7] Introduce automatic DMA configuration for IOMMU masters
Date: Tue, 02 Sep 2014 15:11:23 +0200 [thread overview]
Message-ID: <5405C1FB.6090009@samsung.com> (raw)
In-Reply-To: <4561708.C5IqxBT0S9@wuerfel>
On 2014-09-02 14:46, Arnd Bergmann wrote:
> On Tuesday 02 September 2014 14:30:36 Marek Szyprowski wrote:
>>>>>> However we also need to figure out how to let drivers to make their own
>>>>>> configuration, like it is required by Exynos DRM subsystem, which consist
>>>>>> of several devices, each having its own IOMMU controller, but for
>>>>>> convenience those drivers assume that they all have been bound to the same,
>>>>>> single domain.
>>>>> IIRC with the way we ended up putting the mask into the iommu descriptor of
>>>>> the ARM SMMU, you can put multiple devices into the same iommu group, and
>>>>> have them automatically share a domain.
>>>>>
>>>>> I don't know if the same would work for the Samsung implementation.
>>>> The question is how to transfer such information from the device
>>>> drivers, that
>>>> need/benefit from such configuration to iommu driver, which does all the
>>>> setup?
>>>> This is something completely internal to particular drivers and should
>>>> not be
>>>> exported to device tree or userspace. Thierry suggested to hardcode this
>>>> information in the iommu driver, but I'm looking for other approaches.
>>>> Maybe simply releasing device from the default dma-mapping domain before
>>>> attaching to custom one will be the easiest solution.
>>> For the ARM SMMU, the problem is that there is not necessarily a good way
>>> to partition the masters into IOMMU groups automatically, therefore we
>>> want to provide some hints in DT. On a machine that can have more domains
>>> than it has masters, this is not a problem and we can always use an
>>> all-ones mask, but for a machine on which this is not the case, the
>>> problem is simplified a lot of we hardcode the masks in a way that can
>>> always work, putting multiple devices into an iommu group if necessary.
>> Well, I was talking about the Exynos IOMMU case, where there are no hw
>> restrictions and grouping is done just to make things easier for the Exynos
>> DRM drivers (a buffer gets the same DMA address for all devices, which
>> are a part of virtual Exynos DRM device).
> Does that mean you don't actually need to use multiple contexts here and
> could actually just use the normal dma-mapping interface if there is
> a way to ensure the mappings are always shared across these masters?
Well, a default, shared single domain for dma-mapping interface will work
with Exynos DRM and its multiple masters, although I never thought about
such configuration.
> Or do you need this in addition to being able to use multiple masters
> so you can have multiple rendering contexts in user space?
Such advanced IO space management is not yet implemented.
However there are also devices (like multimedia codec - exynos mfc and
camera
capture subsystem exynos isp), which have limited DMA/IO window (256MiB in
case of video codec), so they will still need to use their own separate
domain.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
prev parent reply other threads:[~2014-09-02 13:11 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-29 15:54 [RFC PATCH 0/7] Introduce automatic DMA configuration for IOMMU masters Will Deacon
2014-08-29 15:54 ` [RFC PATCH 1/7] iommu: provide early initialisation hook for IOMMU drivers Will Deacon
2014-09-01 7:52 ` Thierry Reding
2014-09-01 14:31 ` Arnd Bergmann
2014-09-01 16:36 ` Will Deacon
2014-09-02 6:56 ` Laurent Pinchart
2014-09-02 14:47 ` Varun Sethi
2014-09-02 15:04 ` Arnd Bergmann
2014-08-29 15:54 ` [RFC PATCH 2/7] dma-mapping: replace set_arch_dma_coherent_ops with arch_setup_dma_ops Will Deacon
2014-09-01 14:27 ` Arnd Bergmann
2014-09-01 16:20 ` Will Deacon
2014-08-29 15:54 ` [RFC PATCH 3/7] iommu: add new iommu_ops callback for adding a device with a set of IDs Will Deacon
2014-09-01 8:13 ` Thierry Reding
2014-09-01 14:39 ` Arnd Bergmann
2014-09-01 16:34 ` Will Deacon
2014-09-01 17:18 ` Arnd Bergmann
2014-08-29 15:54 ` [RFC PATCH 4/7] iommu: provide helper function to configure an IOMMU for an of master Will Deacon
2014-09-01 8:29 ` Thierry Reding
2014-09-01 14:46 ` Arnd Bergmann
2014-09-01 16:40 ` Will Deacon
2014-09-01 20:18 ` Arnd Bergmann
2014-09-02 10:03 ` Will Deacon
2014-09-02 12:15 ` Arnd Bergmann
2014-09-02 13:05 ` Will Deacon
2014-09-02 14:01 ` Arnd Bergmann
2014-09-02 20:59 ` jroedel at suse.de
2014-09-03 9:45 ` Will Deacon
2014-09-02 15:03 ` Varun Sethi
2014-09-02 15:08 ` Arnd Bergmann
2014-09-02 10:23 ` Laurent Pinchart
2014-09-02 10:51 ` Laurent Pinchart
2014-09-02 11:03 ` Will Deacon
2014-09-02 19:08 ` Laurent Pinchart
2014-09-02 14:55 ` Varun Sethi
2014-08-29 15:54 ` [RFC PATCH 5/7] dma-mapping: detect and configure IOMMU in of_dma_configure Will Deacon
2014-09-01 14:53 ` Arnd Bergmann
2014-08-29 15:54 ` [RFC PATCH 6/7] arm: call iommu_init before of_platform_populate Will Deacon
2014-08-29 15:54 ` [RFC PATCH 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops Will Deacon
2014-09-02 6:26 ` [RFC PATCH 0/7] Introduce automatic DMA configuration for IOMMU masters Marek Szyprowski
2014-09-02 8:31 ` Will Deacon
2014-09-02 8:48 ` Marek Szyprowski
2014-09-02 8:56 ` Arnd Bergmann
2014-09-02 10:42 ` Marek Szyprowski
2014-09-02 10:57 ` Will Deacon
2014-09-02 12:24 ` Marek Szyprowski
2014-09-02 12:43 ` Arnd Bergmann
2014-09-02 21:50 ` Laurent Pinchart
2014-09-02 12:22 ` Arnd Bergmann
2014-09-02 12:30 ` Marek Szyprowski
2014-09-02 12:46 ` Arnd Bergmann
2014-09-02 13:11 ` Marek Szyprowski [this message]
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