linux-kernel - Re: [PATCH v2] spmi: Fix controller->node != parent->node breakage

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Message-ID: <58cb6c37-0ea0-4866-a2b1-92cb0f0391a7@gmail.com>
Date: Mon, 13 Jan 2025 23:12:28 +0100
From: Konrad Dybcio <konradybcio@...il.com>
To: Stephen Boyd <sboyd@...nel.org>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Joe Hattori <joe@...is.s.u-tokyo.ac.jp>,
 Konrad Dybcio <konradybcio@...nel.org>,
 Matthias Brugger <matthias.bgg@...il.com>,
 Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc: Marijn Suijten <marijn.suijten@...ainline.org>,
 linux-kernel@...r.kernel.org,
 Bjorn Andersson <bjorn.andersson@....qualcomm.com>,
 Abel Vesa <abel.vesa@...aro.org>, Johan Hovold <johan+linaro@...nel.org>,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org,
 Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH v2] spmi: Fix controller->node != parent->node breakage



On 1/13/25 22:52, Stephen Boyd wrote:
> Quoting Konrad Dybcio (2025-01-13 05:02:58)
>> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>>
>> On some platforms, like recent Qualcomm SoCs with multi-bus SPMI
>> arbiters, controller->node must be assigned to the individual buses'
>> subnodes, as the slave devices are children of these, like so:
>>
>> arbiter@...0000
>>          spmi@...d000
>>                  pmic@0
>>
>>          spmi@...2000
>>                  pmic@0
>>
>> The commit referenced in Fixes changed that assignment, such that
>> spmi_controller_alloc() always assumes the PMICs come directly under
>> the arbiter node (which is true when there's only a single bus per
>> controller).
>>
>> Make controller->node specifiable to both benefit from Joe's refcount
>> improvements and un-break the aforementioned platforms.
> 
> How is it broken? I see spmi_pmic_arb_bus_init() calls
> devm_spmi_controller_alloc() which sets the of_node to the parent device
> and then spmi_pmic_arb_bus_init() overwrites that with
> 'ctrl->dev.of_node = node' later on in the same function. That will
> cause one more of_node_put() than is expected. I don't see that removed
> in this patch though, so the leak is still there?
> 
>>
>> Fixes: 821b07853e32 ("spmi: hisi-spmi-controller: manage the OF node reference in device initialization and cleanup")
> 
> I've dropped this patch from my queue. I don't know if we're really
> doing anything better by managing the of_node lifetime in that function
> vs. letting the callers assign the node they want and manage the
> lifetime themselves. Maybe we don't need to do anything? Presumably the
> parent device driver will unregister the controller anyway, so the
> lifetime of the of_node will be ensured regardless. For subnodes like
> qcom SPMI, the subnodes are child nodes of the parent device so they
> won't be removed. If they are dynamic nodes, then the caller can manage
> the lifetime.

Stephen, the wrong node gets assigned in the qcom driver with
multi-master controllers, resulting in probe failures.

Since the introduction of the commit referenced in fixes,
of_spmi_register_devices() sees the controller's subnodes
(which describe each of the two masters) as slave devices
- meaning no "real" devices ever get to probe

Konrad