Re: [PATCH v3 1/7] dt-bindings: interconnect: Add a dma interconnect name

[Maxime Ripard <maxime.ripard@bootlin.com>]

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On Thu, Mar 07, 2019 at 05:15:20PM +0200, Georgi Djakov wrote:
> Hi,
> 
> On 3/5/19 18:14, Robin Murphy wrote:
> > On 05/03/2019 15:53, Maxime Ripard wrote:
> >> Hi,
> >>
> >> On Fri, Mar 01, 2019 at 07:48:15PM +0200, Georgi Djakov wrote:
> >>> On 2/11/19 17:02, Maxime Ripard wrote:
> >>>> The current DT bindings assume that the DMA will be performed by the
> >>>> devices through their parent DT node, and rely on that assumption
> >>>> for the
> >>>> address translation using dma-ranges.
> >>>>
> >>>> However, some SoCs have devices that will perform DMA through
> >>>> another bus,
> >>>> with separate address translation rules. We therefore need to
> >>>> express that
> >>>> relationship, through the special interconnect name "dma".
> >>>>
> >>>> Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
> >>>> ---
> >>>>   Documentation/devicetree/bindings/interconnect/interconnect.txt |
> >>>> 3 +++
> >>>>   1 file changed, 3 insertions(+)
> >>>>
> >>>> diff --git
> >>>> a/Documentation/devicetree/bindings/interconnect/interconnect.txt
> >>>> b/Documentation/devicetree/bindings/interconnect/interconnect.txt
> >>>> index 5a3c575b387a..e69fc2d992c3 100644
> >>>> --- a/Documentation/devicetree/bindings/interconnect/interconnect.txt
> >>>> +++ b/Documentation/devicetree/bindings/interconnect/interconnect.txt
> >>>> @@ -51,6 +51,9 @@ interconnect-names : List of interconnect path
> >>>> name strings sorted in the same
> >>>>                interconnect-names to match interconnect paths with
> >>>> interconnect
> >>>>                specifier pairs.
> >>>>   +                     Reserved interconnect names:
> >>>> +                         * dma: Path from the device to the main
> >>>> memory of the system
> >>>
> >>> Bikeshed: As it's from the device to the main memory, maybe here we can
> >>> also denote this my calling the path dma-mem or dma-memory. For other
> >>> paths, we are trying to mention both the source and the destination and
> >>> maybe it would be good to be consistent although this is special one.
> >>
> >> I'm not sure I understand what you mean. You'd like two interconnect
> >> names, one called dma-memory, and one memory-dma?
> > 
> > Hmm, yes, it's not like "dma" describes an actual source or destination
> > either :/
> 
> IIUC, it's a path (bus) that a dma device use to access some memory
> (read or/and write). So i have used source-destination above more in the
> sense of initiator-target or master-slave. My suggestion was just to
> change the reserved interconnect name from "dma" to "dma-mem" or
> "dma-memory".

If dma is an issue in itself, maybe we can call it "device-memory" ?

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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