linux-kernel - Re: [RFC PATCH 1/3] of/pci: dma-ranges to account highest possible host bridge dma

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Date:   Tue, 28 Mar 2017 09:13:12 -0500
From:   Rob Herring <robh@...nel.org>
To:     Oza Oza <oza.oza@...adcom.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "bcm-kernel-feedback-list@...adcom.com" 
        <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [RFC PATCH 1/3] of/pci: dma-ranges to account highest possible
 host bridge dma_mask

On Tue, Mar 28, 2017 at 12:27 AM, Oza Oza <oza.oza@...adcom.com> wrote:
> On Mon, Mar 27, 2017 at 8:16 PM, Rob Herring <robh@...nel.org> wrote:
>> On Sat, Mar 25, 2017 at 12:31 AM, Oza Pawandeep <oza.oza@...adcom.com> wrote:
>>> it is possible that PCI device supports 64-bit DMA addressing,
>>> and thus it's driver sets device's dma_mask to DMA_BIT_MASK(64),
>>> however PCI host bridge may have limitations on the inbound
>>> transaction addressing. As an example, consider NVME SSD device
>>> connected to iproc-PCIe controller.
>>>
>>> Currently, the IOMMU DMA ops only considers PCI device dma_mask
>>> when allocating an IOVA. This is particularly problematic on
>>> ARM/ARM64 SOCs where the IOMMU (i.e. SMMU) translates IOVA to
>>> PA for in-bound transactions only after PCI Host has forwarded
>>> these transactions on SOC IO bus. This means on such ARM/ARM64
>>> SOCs the IOVA of in-bound transactions has to honor the addressing
>>> restrictions of the PCI Host.
>>>
>>> current pcie frmework and of framework integration assumes dma-ranges
>>> in a way where memory-mapped devices define their dma-ranges.
>>> dma-ranges: (child-bus-address, parent-bus-address, length).
>>>
>>> but iproc based SOCs and even Rcar based SOCs has PCI world dma-ranges.
>>> dma-ranges = <0x43000000 0x00 0x00 0x00 0x00 0x80 0x00>;
>>
>> If you implement a common function, then I expect to see other users
>> converted to use it. There's also PCI hosts in arch/powerpc that parse
>> dma-ranges.
>
> the common function should be similar to what
> of_pci_get_host_bridge_resources is doing right now.
> it parses ranges property right now.
>
> the new function would look look following.
>
> of_pci_get_dma_ranges(struct device_node *dev, struct list_head *resources)
> where resources would return the dma-ranges.
>
> but right now if you see the patch, of_dma_configure calls the new
> function, which actually returns the largest possible size.
> so this new function has to be generic in a way where other PCI hosts
> can use it. but certainly iproc(Broadcom SOC) , rcar based SOCs can
> use it for sure.
>
> although having powerpc using it;  is a separate exercise, since I do
> not have any access to other PCI hosts such as powerpc. but we can
> workout with them on thsi forum if required.

You don't need h/w. You can analyze what parts are common, write
patches to convert to common implementation, and build test. The PPC
and rcar folks can test on h/w.

Rob