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

From: Georgi Djakov <georgi.djakov@linaro.org>
To: Robin Murphy <robin.murphy@arm.com>,
	Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Arnd Bergmann <arnd@arndb.de>,
	dri-devel@lists.freedesktop.org,
	Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
	Chen-Yu Tsai <wens@csie.org>, Rob Herring <robh+dt@kernel.org>,
	Yong Deng <yong.deng@magewell.com>,
	Frank Rowand <frowand.list@gmail.com>,
	Dave Martin <dave.martin@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 1/7] dt-bindings: interconnect: Add a dma interconnect name
Date: Thu, 7 Mar 2019 17:15:20 +0200	[thread overview]
Message-ID: <477995b0-9ac3-b6ca-f5f2-856e4af926f1@linaro.org> (raw)
In-Reply-To: <0e72fbf7-b100-ddc5-3c19-32f71c37f76f@arm.com>

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".

Thanks,
Georgi

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