linux-kernel - Re: [RFC PATCH] interconnect: qcom: add functions to query addr/cmds for a path

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Message-ID: <20200713172241.GB3815@jcrouse1-lnx.qualcomm.com>
Date:   Mon, 13 Jul 2020 11:22:41 -0600
From:   Jordan Crouse <jcrouse@...eaurora.org>
To:     Georgi Djakov <georgi.djakov@...aro.org>
Cc:     Jonathan Marek <jonathan@...ek.ca>, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        kbuild test robot <lkp@...el.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <dri-devel@...ts.freedesktop.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <freedreno@...ts.freedesktop.org>,
        "open list:INTERCONNECT API" <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH] interconnect: qcom: add functions to query addr/cmds
 for a path

On Mon, Jul 13, 2020 at 06:24:26PM +0300, Georgi Djakov wrote:
> On 7/1/20 07:25, Jonathan Marek wrote:
> > The a6xx GMU can vote for ddr and cnoc bandwidth, but it needs to be able
> > to query the interconnect driver for bcm addresses and commands.
> 
> It's not very clear to me how the GMU firmware would be dealing with this? Does
> anyone have an idea whether the GMU makes any bandwidth decisions? Or is it just
> a static configuration and it just enables/disables a TCS?

The GMU can perform a direct vote to the hardware. For now it is a static
configuration with pre-determined bandwidths generated from the OPP table.

> I think that we can query the address from the cmd-db, but we have to know the
> bcm names and the path. All the BCM/TCS information looks to be very low-level
> and implementation specific, so exposing it through an API is not very good,
> but hard-coding all this information is not good either.

Exactly my concern. The BCM information in particular is going to end up being
extremely target specific.

Jordan

> Thanks,
> Georgi
> 
> > 
> > I'm not sure what is the best way to go about implementing this, this is
> > what I came up with.
> > 
> > I included a quick example of how this can be used by the a6xx driver to
> > fill out the GMU bw_table (two ddr bandwidth levels in this example, note
> > this would be using the frequency table in dts and not hardcoded values).
> > 
> > Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> > ---
> >  drivers/gpu/drm/msm/adreno/a6xx_hfi.c | 20 ++++-------
> >  drivers/interconnect/qcom/icc-rpmh.c  | 50 +++++++++++++++++++++++++++
> >  include/soc/qcom/icc.h                | 11 ++++++
> >  3 files changed, 68 insertions(+), 13 deletions(-)

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