linux-kernel - Re: [PATCH v4 0/7] OPP: Add support to find OPP for a set of keys

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Message-ID: <aKyS0RGZX4bxbjDj@hu-wasimn-hyd.qualcomm.com>
Date: Mon, 25 Aug 2025 22:14:01 +0530
From: Wasim Nazir <wasim.nazir@....qualcomm.com>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 0/7] OPP: Add support to find OPP for a set of keys

On Wed, Aug 20, 2025 at 01:58:46PM +0530, Krishna Chaitanya Chundru wrote:
> The existing OPP table in the device tree for PCIe is shared across
> different link configurations such as data rates 8GT/s x2 and 16GT/s x1.
> These configurations often operate at the same frequency, allowing them
> to reuse the same OPP entries. However, 8GT/s and 16 GT/s may have
> different characteristics beyond frequency—such as RPMh votes in QCOM
> case, which cannot be represented accurately when sharing a single OPP.
> 
> In such cases, frequency alone is not sufficient to uniquely identify
> an OPP. To support these scenarios, introduce a new API
> dev_pm_opp_find_key_exact() that allows OPP lookup for set of keys like
> frequency, level & bandwidth.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---
> Changes in v4:
> - Included dtsi changes for all platforms.
> - Made the changes as requested by Viresh like adding comments, some
>   coding styles etc.
> - Link to v3: https://lore.kernel.org/r/20250819-opp_pcie-v3-0-f8bd7e05ce41@oss.qualcomm.com
> 
> Changes in v3:
> - Always check for frequency match unless user doesn't pass it (Viresh).
> - Make dev_pm_opp_key public and let user pass the key (Viresh).
> - Include bandwidth as part of dev_pm_opp_key (Viresh).
> - Link to v2: https://lore.kernel.org/r/20250818-opp_pcie-v2-0-071524d98967@oss.qualcomm.com
> 
> Changes in v2:
> - Use opp-level to indentify data rate and use both frequency and level
>   to identify the OPP. (Viresh)
> - Link to v1: https://lore.kernel.org/r/20250717-opp_pcie-v1-0-dde6f452571b@oss.qualcomm.com
> 
> ---
> Krishna Chaitanya Chundru (7):
>       OPP: Add support to find OPP for a set of keys
>       OPP: Move refcount and key update for readability in _opp_table_find_key()

Hi Krishna,

Patch 2/7 is applied in linux-next (20250825) as commit
b5323835f050 (OPP: Reorganize _opp_table_find_key()) which is causing
regression on my board (lemans-evk (arm64)).
Reverting the change is resolving the issue.

Kernel log:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000016
...
Call trace:
 _read_bw+0x0/0x10 (P)
 _find_key+0xb8/0x194
 dev_pm_opp_find_bw_floor+0x54/0x8c
 bwmon_intr_thread+0x84/0x284 [icc_bwmon]
 irq_thread_fn+0x2c/0xa8
 irq_thread+0x174/0x334
 kthread+0x134/0x208
 ret_from_fork+0x10/0x20

>       arm64: dts: qcom: sm8450: Add opp-level to indicate PCIe data rates
>       arm64: dts: qcom: sm8550: Add opp-level to indicate PCIe data rates
>       arm64: dts: qcom: sm8650: Add opp-level to indicate PCIe data rates
>       arm64: dts: qcom: x1e80100: Add opp-level to indicate PCIe data rates
>       PCI: qcom: Use frequency and level based OPP lookup
> 
>  arch/arm64/boot/dts/qcom/sm8450.dtsi   |  41 ++++++++++---
>  arch/arm64/boot/dts/qcom/sm8550.dtsi   |  63 ++++++++++++++-----
>  arch/arm64/boot/dts/qcom/sm8650.dtsi   |  63 ++++++++++++++-----
>  arch/arm64/boot/dts/qcom/x1e80100.dtsi |  90 ++++++++++++++++++++++-----
>  drivers/opp/core.c                     | 107 +++++++++++++++++++++++++++++++--
>  drivers/pci/controller/dwc/pcie-qcom.c |   7 ++-
>  include/linux/pm_opp.h                 |  30 +++++++++
>  7 files changed, 341 insertions(+), 60 deletions(-)
> ---
> base-commit: c17b750b3ad9f45f2b6f7e6f7f4679844244f0b9
> change-id: 20250717-opp_pcie-793160b2b113
> 
> Best regards,
> -- 
> Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> 

-- 
Regards,
Wasim