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

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Message-ID: <9f0628df-26b2-6ec8-3868-b2f72f0c8918@marek.ca>
Date:   Mon, 13 Jul 2020 11:33:39 -0400
From:   Jonathan Marek <jonathan@...ek.ca>
To:     Georgi Djakov <georgi.djakov@...aro.org>,
        linux-arm-msm@...r.kernel.org
Cc:     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>,
        Jordan Crouse <jcrouse@...eaurora.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 7/13/20 11:24 AM, 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 is able to vote for bandwidth, and presumably RPMh is 
aggregating those votes with the votes from the interconnect driver. We 
need to be able to fill out the "struct a6xx_hfi_msg_bw_table" in 
drivers/gpu/drm/msm/adreno/a6xx_hfi.h, which has a table of DDR 
bandwidth cmds which can be selected when changing the GPU frequency 
(the bw field in a6xx_hfi_gx_bw_perf_vote_cmd).

 From Jordan: "the GMU registers a bus vote directly with the hardware. 
It should handle aggregation for us."

> 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.
> 
> 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(-)