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

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Message-ID: <14c1f547-31de-6c7c-2b37-2c902f9d3d78@arm.com>
Date:   Thu, 3 Aug 2017 18:21:33 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Nate Watterson <nwatters@...eaurora.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-acpi@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Will Deacon <will.deacon@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>, Feng Kan <fkan@....com>,
        Jon Masters <jcm@...hat.com>,
        Robert Moore <robert.moore@...el.com>,
        Zhang Rui <rui.zhang@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v3 0/5] ACPI: DMA ranges management

On 03/08/17 16:45, Nate Watterson wrote:
> Hi Lorenzo,
> 
> On 8/3/2017 8:32 AM, Lorenzo Pieralisi 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(-)
>>
> 
> I tested with named components and with _DMA objects at a variety of
> sizes and verified the configured masks matched the expected values.
> 
> Tested-by: Nate Watterson <nwatters@...eaurora.org>
> 
> One general question I had while testing the patch is whether it is
> possible to define a complete 64-bit range using the _DMA method. For
> instance, to get a 64-bit dma_mask I had to use a non-zero MIN value
> so that LEN would not overflow.

As far as I understand ACPI, all addresses are at most 64-bit. Thus the
only valid DMA range of size 2^64 would be one with a minimum of 0 and
no offset, and that can already be described by the simple absence of a
_DMA object.

Robin.

> 
> QWORDMemory(
>     ResourceConsumer,
>     PosDecode,       // _DEC
>     MinFixed,        // _MIF
>     MaxFixed,        // _MAF
>     Prefetchable,    // _MEM
>     ReadWrite,       // _RW
>     0,               // _GRA
>     0x1000,               // _MIN
>     0xffffffffffffffff,   // _MAX
>     0x0,                  // _TRA
>     0xfffffffffffff000,   // _LEN
>     ,
>     ,
>     ,
> )
> 
> -Nate
>