Messages in this thread | | | Subject | Re: [PATCH 00/11] of: Fix DMA configuration for non-DT masters | From | Robin Murphy <> | Date | Wed, 25 Sep 2019 17:52:39 +0100 |
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On 25/09/2019 17:16, Rob Herring wrote: > On Wed, Sep 25, 2019 at 10:30 AM Nicolas Saenz Julienne > <nsaenzjulienne@suse.de> wrote: >> >> On Wed, 2019-09-25 at 16:09 +0100, Robin Murphy wrote: >>> On 25/09/2019 15:52, Nicolas Saenz Julienne wrote: >>>> On Tue, 2019-09-24 at 16:59 -0500, Rob Herring wrote: >>>>> On Tue, Sep 24, 2019 at 1:12 PM Nicolas Saenz Julienne >>>>> <nsaenzjulienne@suse.de> wrote: >>>>>> Hi All, >>>>>> this series tries to address one of the issues blocking us from >>>>>> upstreaming Broadcom's STB PCIe controller[1]. Namely, the fact that >>>>>> devices not represented in DT which sit behind a PCI bus fail to get the >>>>>> bus' DMA addressing constraints. >>>>>> >>>>>> This is due to the fact that of_dma_configure() assumes it's receiving a >>>>>> DT node representing the device being configured, as opposed to the PCIe >>>>>> bridge node we currently pass. This causes the code to directly jump >>>>>> into PCI's parent node when checking for 'dma-ranges' and misses >>>>>> whatever was set there. >>>>>> >>>>>> To address this I create a new API in OF - inspired from Robin Murphys >>>>>> original proposal[2] - which accepts a bus DT node as it's input in >>>>>> order to configure a device's DMA constraints. The changes go deep into >>>>>> of/address.c's implementation, as a device being having a DT node >>>>>> assumption was pretty strong. >>>>>> >>>>>> On top of this work, I also cleaned up of_dma_configure() removing its >>>>>> redundant arguments and creating an alternative function for the special >>>>>> cases >>>>>> not applicable to either the above case or the default usage. >>>>>> >>>>>> IMO the resulting functions are more explicit. They will probably >>>>>> surface some hacky usages that can be properly fixed as I show with the >>>>>> DT fixes on the Layerscape platform. >>>>>> >>>>>> This was also tested on a Raspberry Pi 4 with a custom PCIe driver and >>>>>> on a Seattle AMD board. >>>>> >>>>> Humm, I've been working on this issue too. Looks similar though yours >>>>> has a lot more churn and there's some other bugs I've found. >>>> >>>> That's good news, and yes now that I see it, some stuff on my series is >>>> overly >>>> complicated. Specially around of_translate_*(). >>>> >>>> On top of that, you removed in of_dma_get_range(): >>>> >>>> - /* >>>> - * At least empty ranges has to be defined for parent node if >>>> - * DMA is supported >>>> - */ >>>> - if (!ranges) >>>> - break; >>>> >>>> Which I assumed was bound to the standard and makes things easier. >>>> >>>>> Can you test out this branch[1]. I don't have any h/w needing this, >>>>> but wrote a unittest and tested with modified QEMU. >>>> >>>> I reviewed everything, I did find a minor issue, see the patch attached. >>> >>> WRT that patch, the original intent of "force_dma" was purely to >>> consider a device DMA-capable regardless of the presence of >>> "dma-ranges". Expecting of_dma_configure() to do anything for a non-OF >>> device has always been bogus - magic paravirt devices which appear out >>> of nowhere and expect to be treated as genuine DMA masters are a >>> separate problem that we haven't really approached yet. >> >> I agree it's clearly abusing the function. I have no problem with the behaviour >> change if it's OK with you.
Thinking about it, you could probably just remove that call from the Xen DRM driver now anyway - since the dma-direct rework, we lost the ability to set dma_dummy_ops by default, and NULL ops now represent what it (presumably) wants.
>> Robin, have you looked into supporting multiple dma-ranges? It's the next thing >> we need for BCM STB's PCIe. I'll have a go at it myself if nothing is in the >> works already. > > Multiple dma-ranges as far as configuring inbound windows should work > already other than the bug when there's any parent translation. But if > you mean supporting multiple DMA offsets and masks per device in the > DMA API, there's nothing in the works yet.
There's also the in-between step of making of_dma_get_range() return a size based on all the dma-ranges entries rather than only the first one - otherwise, something like [1] can lead to pretty unworkable default masks. We implemented that when doing acpi_dma_get_range(), it's just that the OF counterpart never caught up.
Robin.
[1] http://linux-arm.org/git?p=linux-rm.git;a=commitdiff;h=a2814af56b3486c2985a95540a88d8f9fa3a699f
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