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SubjectRe: [RFC PATCH 0/2] Add sideband data extraction
On Fri, Jul 07, 2017 at 12:39:57PM +0530, Srinath Mannam wrote:
> These patches implements optional DT properties to generate
> smaller sideband data from RID which can be further mapped
> to MSI Device ID or Stream ID
>
> On some of the systems, sideband data is smaller than RID
> (16bits). For such system, sideband data has to be generated
> by dropping some of the RID bits
>
> the process of sideband data extracted from RID can be expressed
> using optional DT property {iommu/msi}-map-drop-mask.
>
> Example: If drop-mask is 0xFF09 then sideband data is
> 8 bits bus number followed by 1 bit of device number and
> 1 bit function number. This means drop-mask=0xFF09 will
> convert RID=0x1a10 (16bits) to sideband data 0x6a (10bits).

So IIUC, here's you're using this not only to mask bits out, but also to
determine a *shift* to apply to the value, implicitly provided by the
(contiguous) low bits of the mask.

That's really not obvious from the name.

Mark.

>
> Srinath Mannam (2):
> dt-bindings: pci: Add drop mask property for MSI and IOMMU
> pcie: sideband data by dropping RID bits
>
> .../devicetree/bindings/pci/pci-iommu.txt | 31 ++++++++++++++
> Documentation/devicetree/bindings/pci/pci-msi.txt | 33 +++++++++++++++
> drivers/iommu/of_iommu.c | 4 +-
> drivers/of/irq.c | 3 +-
> drivers/of/of_pci.c | 48 ++++++++++++++++++++--
> include/linux/of_pci.h | 6 ++-
> 6 files changed, 117 insertions(+), 8 deletions(-)
>
> --
> 2.7.4
>

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