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Message-ID: <610d5d7c-ec8d-42f1-81a2-1376b8a1a43f@linaro.org>
Date: Thu, 1 Feb 2024 15:45:17 +0100
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Subject: Re: [PATCH v6 5/6] arm64: dts: qcom: sm8450: Add opp table support to
 PCIe
To: Viresh Kumar <viresh.kumar@linaro.org>,
 Manivannan Sadhasivam <mani@kernel.org>
Cc: Krishna chaitanya chundru <quic_krichai@quicinc.com>,
 Bjorn Andersson <andersson@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
 Lorenzo Pieralisi <lpieralisi@kernel.org>,
 =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= <kw@linux.com>,
 Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
 Conor Dooley <conor+dt@kernel.org>, Rob Herring <robh+dt@kernel.org>,
 Johan Hovold <johan+linaro@kernel.org>, Brian Masney <bmasney@redhat.com>,
 Georgi Djakov <djakov@kernel.org>, linux-arm-msm@vger.kernel.org,
 vireshk@kernel.org, quic_vbadigan@quicinc.com, quic_skananth@quicinc.com,
 quic_nitegupt@quicinc.com, linux-pci@vger.kernel.org,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20240112-opp_support-v6-0-77bbf7d0cc37@quicinc.com>
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 <20240130083619.lqbj47fl7aa5j3k5@vireshk-i7>
 <20240130094804.GD83288@thinkpad>
 <20240130095508.zgufudflizrpxqhy@vireshk-i7> <20240130131625.GA2554@thinkpad>
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From: Konrad Dybcio <konrad.dybcio@linaro.org>
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On 31.01.2024 06:23, Viresh Kumar wrote:
> On 30-01-24, 18:46, Manivannan Sadhasivam wrote:
>> Agree. But what I'm saying is, right now there is no DT property in the
>> interconnect consumer nodes to specificy the bw requirements. This is all
>> hardcoded in the respective ICC consumer drivers.
> 
> I thought there are a lot of users already in there..
> 
> $ git grep -i opp.*bps arch/arm64/boot/dts/ | wc -l
> 864
> 
>> But when we use OPP to control bw, the bw requirements come from DT. This is
>> what I see as a difference. Because, only nodes making use of OPP will specify
>> bw in DT and other nodes making use of just ICC will not.
>>
>> Maybe I'm worrying too much about these details... But it looks like
>> inconsistency to me.
> 
> Right. So is there inconsistency right now ? Yes, there is.
> 
> The important question we need to answer is where do we want to see
> all these drivers (specially new ones) in the future. What's the right
> thing to do eventually ? Hardcode stuff ? Or Move it to DT ?
> 
> The answer is DT for me, so the code can be generic enough to be
> reused. This is just one step in the right direction I guess.
> Eventually the drivers must get simplified, which they are I guess.

I'm lukewarm on this.

A *lot* of hardware has more complex requirements than "x MBps at y MHz",
especially when performance counters come into the picture for dynamic
bw management.

OPP tables can't really handle this properly.

Konrad