linux-kernel - Re: [PATCH v3 0/5] ACPI: DMA ranges management

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Message-ID: <20171201103943.GA25066@red-moon>
Date:   Fri, 1 Dec 2017 10:39:43 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Feng Kan <fkan@....com>
Cc:     "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Will Deacon <will.deacon@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Jon Masters <jcm@...hat.com>,
        Robert Moore <robert.moore@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Zhang Rui <rui.zhang@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Nate Watterson <nwatters@...eaurora.org>
Subject: Re: [PATCH v3 0/5] ACPI: DMA ranges management

On Thu, Nov 30, 2017 at 04:43:00PM -0800, Feng Kan wrote:
> On Wed, Nov 29, 2017 at 11:28 PM, Feng Kan <fkan@....com> wrote:
> > On Thu, Aug 3, 2017 at 5:32 AM, Lorenzo Pieralisi
> > <lorenzo.pieralisi@....com> wrote:
> >> This patch series is v3 of a previous posting:
> >>
> >> v2->v3:
> >>         - Fixed DMA masks computation
> >>         - Fixed size computation overflow in acpi_dma_get_range()
> >>
> >> v1->v2:
> >>         - Reworked acpi_dma_get_range() flow and logs
> >>         - Added IORT named component address limits
> >>         - Renamed acpi_dev_get_resources() helper function
> >>         - Rebased against v4.13-rc3
> >>
> >> v2: http://lkml.kernel.org/r/20170731152323.32488-1-lorenzo.pieralisi@arm.com
> >> v1: http://lkml.kernel.org/r/20170720144517.32529-1-lorenzo.pieralisi@arm.com
> >>
> >> -- Original cover letter --
> >>
> >> As reported in:
> >>
> >> http://lkml.kernel.org/r/CAL85gmA_SSCwM80TKdkZqEe+S1beWzDEvdki1kpkmUTDRmSP7g@mail.gmail.com
> >>
> >> the bus connecting devices to an IOMMU bus can be smaller in size than
> >> the IOMMU input address bits which results in devices DMA HW bugs in
> >> particular related to IOVA allocation (ie chopping of higher address
> >> bits owing to system bus HW capabilities mismatch with the IOMMU).
> >>
> >> Fortunately this problem can be solved through an already present but never
> >> used ACPI 6.2 firmware bindings (ie _DMA object) allowing to define the DMA
> >> window for a specific bus in ACPI and therefore all upstream devices
> >> connected to it.
> >>
> >> This small patch series enables _DMA parsing in ACPI core code and
> >> use it in ACPI IORT code in order to detect DMA ranges for devices and
> >> update their data structures to make them work with their related DMA
> >> addressing restrictions.
> >>
> >> Cc: Will Deacon <will.deacon@....com>
> >> Cc: Hanjun Guo <hanjun.guo@...aro.org>
> >> Cc: Feng Kan <fkan@....com>
> >> Cc: Jon Masters <jcm@...hat.com>
> >> Cc: Robert Moore <robert.moore@...el.com>
> >> Cc: Robin Murphy <robin.murphy@....com>
> >> Cc: Zhang Rui <rui.zhang@...el.com>
> >> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> >>
> >> Lorenzo Pieralisi (5):
> >>   ACPICA: resource_mgr: Allow _DMA method in walk resources
> >>   ACPI: Make acpi_dev_get_resources() method agnostic
> >>   ACPI: Introduce DMA ranges parsing
> >>   ACPI: Make acpi_dma_configure() DMA regions aware
> >>   ACPI/IORT: Add IORT named component memory address limits
> >>
> >>  drivers/acpi/acpica/rsxface.c |  7 ++--
> >>  drivers/acpi/arm64/iort.c     | 57 ++++++++++++++++++++++++++-
> >>  drivers/acpi/resource.c       | 82 +++++++++++++++++++++++++++++---------
> >>  drivers/acpi/scan.c           | 91 +++++++++++++++++++++++++++++++++++++++----
> >>  include/acpi/acnames.h        |  1 +
> >>  include/acpi/acpi_bus.h       |  2 +
> >>  include/linux/acpi.h          |  8 ++++
> >>  include/linux/acpi_iort.h     |  5 ++-
> >>  8 files changed, 219 insertions(+), 34 deletions(-)
> >>
> >> --
> >> 2.10.0
> >>
> > Lorenzo:
> >
> > A network driver can use pci_set_dma_mask or its like to override what
> > is done with this patch here.
> > Which would result in iova allocation greater than the original _DMA
> > aperture. Should we force
> > the dma_set_mask to not change if an existing mask is already set?
> 
> Let me clarify the question some more, in our system the IOMMU supports only
> 42 bits of address. With your _DMA aperture patch, the initial dma_mask and
> coherent_mask are correctly set by the code. However, the device driver can
> set the dma_mask and coherent mask at a later point which over writes the
> initial setting by your code. In which case, once the iova is exhausted with the
> 32 bit address, it will start seeking more iova address via the
> dma_limit. In this
> case it would fail my system since the iommu.aperture_end is that of 48 bits
> as derived from ias field in  the SMMU.
> 
> Should the dma_limit be the smallest of driver->dma_mask, iommu.aperture_end and
> your _DMA aperture size via ACPI table? Rather than just the
> driver->dma_mask and
> iommu.aperture_end. This will ensure the smallest/correct aperture is used.

IIUC Nate already reported this issue - I will sync with Robin to
check the status of this thread:

https://marc.info/?l=linux-acpi&m=150108156230455&w=2

Thanks,
Lorenzo