linux-kernel - Re: [PATCH v3] interconnect: avoid memory allocation when 'icc_bw

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Message-ID: <84b94649-a248-46b0-a401-772aeb8777a2@gmail.com>
Date: Wed, 25 Jun 2025 15:15:53 +0200
From: Gabor Juhos <j4g8y7@...il.com>
To: Johan Hovold <johan@...nel.org>
Cc: Georgi Djakov <djakov@...nel.org>,
 Raviteja Laggyshetty <quic_rlaggysh@...cinc.com>,
 Johan Hovold <johan+linaro@...nel.org>,
 Bryan O'Donoghue <bryan.odonoghue@...aro.org>, linux-pm@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] interconnect: avoid memory allocation when
 'icc_bw_lock' is held

2025. 06. 25. 14:41 keltezéssel, Johan Hovold írta:
> On Wed, Jun 25, 2025 at 02:30:15PM +0200, Johan Hovold wrote:
>> On Wed, Jun 25, 2025 at 01:25:04PM +0200, Gabor Juhos wrote:
> 
>>> @@ -276,13 +276,17 @@ int qcom_icc_rpmh_probe(struct platform_device *pdev)
>>>  		qcom_icc_bcm_init(qp->bcms[i], dev);
>>>  
>>>  	for (i = 0; i < num_nodes; i++) {
>>> +		bool is_dyn_node = false;
>>> +
>>>  		qn = qnodes[i];
>>>  		if (!qn)
>>>  			continue;
>>>  
>>>  		if (desc->alloc_dyn_id) {
>>> -			if (!qn->node)
>>> +			if (!qn->node) {
>>
>> AFAICS, qn->node will currently never be set here and I'm not sure why
>> commit 7f9560a3bebe ("interconnect: qcom: icc-rpmh: Add dynamic icc node
>> id support") added this check, or even the node field to struct
>> qcom_icc_desc for that matter.
>>
>> But if there's some future use case for this, then you may or may not
>> need to make sure that a name is allocated also in that case.
> 
> Ok, I see what's going on. The qn->node may have been (pre-) allocated
> in icc_link_nodes() dynamically, which means you need to make sure to
> generate a name also in that case.
> 
>> And that could be done by simply checking if node->id >=
>> ICC_DYN_ID_START instead of using a boolean flag below. That may be
>> preferred either way.
> 
> So you should probably use node->id to determine this.

You are right. The problem is that ICC_DYN_ID_START is only visible from the
core code. Either we have to move that into the 'interconnect-provider.h' header
or we have to add an icc_node_is_dynamic() helper or something similar.

Which is the preferred solution?

Regards,
Gabor