linux-kernel - Re: [RFC PATCH] interconnect: Replace of_icc_get() with icc

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Message-ID: <20190925091522.jf5q2jdo6njfkxto@gilmour>
Date:   Wed, 25 Sep 2019 11:15:22 +0200
From:   Maxime Ripard <mripard@...nel.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Georgi Djakov <georgi.djakov@...aro.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Evan Green <evgreen@...omium.org>,
        David Dai <daidavid1@...eaurora.org>
Subject: Re: [RFC PATCH] interconnect: Replace of_icc_get() with icc_get()
 and reduce DT binding

Hi Stephen,

On Tue, Sep 24, 2019 at 10:41:33PM -0700, Stephen Boyd wrote:
> The DT binding could also be simplified somewhat. Currently a path needs
> to be specified in DT for each and every use case that is possible for a
> device to want. Typically the path is to memory, which looks to be
> reserved for in the binding with the "dma-mem" named path, but sometimes
> the path is from a device to the CPU or more generically from a device
> to another device which could be a CPU, cache, DMA master, or another
> device if some sort of DMA to DMA scenario is happening. Let's remove
> the pair part of the binding so that we just list out a device's
> possible endpoints on the bus or busses that it's connected to.
>
> If the kernel wants to figure out what the path is to memory or the CPU
> or a cache or something else it should be able to do that by finding the
> node for the "destination" endpoint, extracting that node's
> "interconnects" property, and deriving the path in software. For
> example, we shouldn't need to write out each use case path by path in DT
> for each endpoint node that wants to set a bandwidth to memory. We
> should just be able to indicate what endpoint(s) a device sits on based
> on the interconnect provider in the system and then walk the various
> interconnects to find the path from that source endpoint to the
> destination endpoint.

The dma-mem name is used by the OF core to adjust the mapping of the
devices as well. So, any solution needs to be generic (or provide a
generic helper).

Maxime

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