linux-kernel - Re: [PATCH 11/13] dtb: amd: Add PCIe SMMU device tree node

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Message-ID: <56FCD43A.4090409@linaro.org>
Date:	Thu, 31 Mar 2016 09:39:38 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Arnd Bergmann <arnd@...db.de>, Mark Rutland <mark.rutland@....com>,
	devicetree@...r.kernel.org, arm@...nel.org, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, linux-kernel@...r.kernel.org,
	robh+dt@...nel.org, leo.duran@....com,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	galak@...eaurora.org, thomas.lendacky@....com,
	Robin Murphy <robin.murphy@....com>,
	linux-arm-kernel@...ts.infradead.org, brijeshkumar.singh@....com,
	Christoffer Dall <christoffer.dall@...aro.org>,
	"eric.auger@...com" <eric.auger@...com>
Subject: Re: [PATCH 11/13] dtb: amd: Add PCIe SMMU device tree node

Hi Will,
On 03/30/2016 07:24 PM, Will Deacon wrote:
> On Wed, Mar 30, 2016 at 05:57:08PM +0200, Eric Auger wrote:
>> On 03/30/2016 05:45 PM, Will Deacon wrote:
>>> On Wed, Mar 30, 2016 at 05:37:27PM +0200, Eric Auger wrote:
>>>> On 01/28/2016 03:27 PM, Will Deacon wrote:
>>>>> On Thu, Jan 28, 2016 at 03:17:33PM +0100, Arnd Bergmann wrote:
>>>>>> On Thursday 28 January 2016 12:20:58 Robin Murphy wrote:
>>>>>>>>
>>>>>>> Any IDs specified here would only apply to DMA by the "platform device" 
>>>>>>> side of the host controller itself (as would an equivalent "iommus" 
>>>>>>> property on pcie0 once I finish the SMMUv2 generic binding support I'm 
>>>>>>> working on). In terms of PCI devices, the "mmu-masters" property is 
>>>>>>> overloaded such that only its existence matters, to identify that there 
>>>>>>> _is_ a relationship between the SMMU and the PCI bus(es) behind that 
>>>>>>> host controller.
>>>>>>
>>>>>> I wasn't aware that this was actually still specified. I had hoped
>>>>>> we were getting rid of mmu-masters before anyone actually started
>>>>>> using it, but now I see it in ns2.dtsi and fsl-ls2080a.dtsi.
>>>>>>
>>>>>> Does anyone know what happened to the plan to use the iommu DT binding
>>>>>> for the ARM SMMU instead? Do we now have to support both ways indefinitely?
>>>>>
>>>>> We always did -- Seattle used the mmu-masters binding before the generic
>>>>> binding even existed. Robin has been working on patches to get of_xlate
>>>>> up and running, but it got held up by Laurent's series which didn't end
>>>>> up going anywhere.
>>>>>
>>>> Up to now I have used the PCI smmu description as described in Suravee's
>>>> patch and this does not work anymore with 4.6-rc1 since the default
>>>> domain was introduced. So now I see 2 SMRs matching a single streamid
>>>> (in my case 256, one steming from the "platform device" side of the host
>>>> controller and one steming from the PCI device) and this causes SMCF
>>>> (stream match conflict fault). So PCIe PF does not work.
>>>
>>> Sorry about that, it wasn't intentional. In fact, I wrote commit
>>> cbf8277ef456 ("iommu/arm-smmu: Treat IOMMU_DOMAIN_DMA as bypass for now")
>>> specifically to avoid this breakage, after seeing it myself with VFIO
>>> and an S2CR-based configuration. It looks like the check just needs moving
>>> higher up (i.e. before we initialise the SMRs).
>>>
>>> Does that fix it for you?
>> Yes this fixes the issue for me, thanks! I guess you will send that patch?
> 
> I need to check that it doesn't break rebinding to the host after VFIO
> has been used for passthrough, first.

OK. I can help testing too since I am currently working on PCIe
passthrough respin.
> 
> Does your devicetree explicitly assign a StreamID to the platform device
> for the host controller? We should probably be handling this, since it
> will crop us as an issue again once we decide to enable the default
> domain properly.

Yes it does. My dt description currently matches the one found in this
patch from Suravee (old binding style). Hence my question. Shall I
remove this and let PCIe register their RID=SID automatically?
> 
>> So eventually what is the right way to describe the smmu-masters (~
>> future of that patch)?
> 
> Using the generic iommu binding
> (Documentation/devicetree/bindings/iommu/iommu.txt), which will be required
> for of_xlate-based probing. The old binding should still continue to
> function as it always has, though.
OK thanks

Eric
> 
> Will
>