linux-kernel - Re: [PATCH v6 1/5] cpuidle: qcom_spm: Detach state machine from main SPM handling

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Message-ID: <YNHR3hvoKsQe5mq8@gerhold.net>
Date:   Tue, 22 Jun 2021 14:04:46 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Cc:     bjorn.andersson@...aro.org, agross@...nel.org,
        daniel.lezcano@...aro.org, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, phone-devel@...r.kernel.org,
        konrad.dybcio@...ainline.org, marijn.suijten@...ainline.org,
        martin.botka@...ainline.org, jeffrey.l.hugo@...il.com,
        jami.kettunen@...ainline.org,
        ~postmarketos/upstreaming@...ts.sr.ht, devicetree@...r.kernel.org,
        robh+dt@...nel.org
Subject: Re: [PATCH v6 1/5] cpuidle: qcom_spm: Detach state machine from main
 SPM handling

On Tue, Jun 22, 2021 at 01:39:15PM +0200, AngeloGioacchino Del Regno wrote:
> Il 21/06/21 23:08, Stephan Gerhold ha scritto:
> > On Mon, Jun 21, 2021 at 08:10:12PM +0200, AngeloGioacchino Del Regno wrote:
> > > In commit a871be6b8eee ("cpuidle: Convert Qualcomm SPM driver to a generic
> > > CPUidle driver") the SPM driver has been converted to a
> > > generic CPUidle driver: that was mainly made to simplify the
> > > driver and that was a great accomplishment;
> > > Though, it was ignored that the SPM driver is not used only
> > > on the ARM architecture.
> > > 
> > 
> > I don't really understand why you insist on writing that I deliberately
> > "ignored" your use case when converting the driver. This is not true.
> > Perhaps that's not actually what you meant but that's how it sounds to
> > me.
> > 
> 
> So much noise for one single word. I will change it since it seems to be
> that much of a deal, and I'm sorry if that hurt you in any way.
> 
> For the records, though, I really don't see anything offensive in that,
> and anyway I didn't mean to be offensive in any way.
> 

I try to put a lot of thought into my patches to make sure I don't
accidentally break some other use cases. Having that sentence in the
commit log does indeed hurt me a bit since I would never deliberately
disregard other use cases without making it absolutely clear in the
patch.

By using the word "ignored" ("deliberately not listen or pay attention
to") [1] you say that I did, and that's why I would prefer if you
reword this slightly. :)

[1] https://en.wiktionary.org/wiki/ignore

> > > In preparation for the enablement of SPM features on AArch64/ARM64,
> > > split the cpuidle-qcom-spm driver in two: the CPUIdle related
> > > state machine (currently used only on ARM SoCs) stays there, while
> > > the SPM communication handling lands back in soc/qcom/spm.c and
> > > also making sure to not discard the simplifications that were
> > > introduced in the aforementioned commit.
> > > 
> > > Since now the "two drivers" are split, the SCM dependency in the
> > > main SPM handling is gone and for this reason it was also possible
> > > to move the SPM initialization early: this will also make sure that
> > > whenever the SAW CPUIdle driver is getting initialized, the SPM
> > > driver will be ready to do the job.
> > > 
> > > Please note that the anticipation of the SPM initialization was
> > > also done to optimize the boot times on platforms that have their
> > > CPU/L2 idle states managed by other means (such as PSCI), while
> > > needing SAW initialization for other purposes, like AVS control.
> > > 
> > > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
> > > ---
> > >   drivers/cpuidle/Kconfig.arm        |   1 +
> > >   drivers/cpuidle/cpuidle-qcom-spm.c | 324 +++++++----------------------
> > >   drivers/soc/qcom/Kconfig           |   9 +
> > >   drivers/soc/qcom/Makefile          |   1 +
> > >   drivers/soc/qcom/spm.c             | 198 ++++++++++++++++++
> > >   include/soc/qcom/spm.h             |  41 ++++
> > >   6 files changed, 325 insertions(+), 249 deletions(-)
> > >   create mode 100644 drivers/soc/qcom/spm.c
> > >   create mode 100644 include/soc/qcom/spm.h
> > > 
> > > diff --git a/drivers/cpuidle/cpuidle-qcom-spm.c b/drivers/cpuidle/cpuidle-qcom-spm.c
> > > index adf91a6e4d7d..091453135ea6 100644
> > > --- a/drivers/cpuidle/cpuidle-qcom-spm.c
> > > +++ b/drivers/cpuidle/cpuidle-qcom-spm.c
> > > [...]
> > > +static int spm_cpuidle_register(int cpu)
> > >   {
> > > +	struct platform_device *pdev = NULL;
> > > +	struct device_node *cpu_node, *saw_node;
> > > +	struct cpuidle_qcom_spm_data data = {
> > > +		.cpuidle_driver = {
> > > +			.name = "qcom_spm",
> > > +			.owner = THIS_MODULE,
> > > +			.cpumask = (struct cpumask *)cpumask_of(cpu),
> > > +			.states[0] = {
> > > +				.enter			= spm_enter_idle_state,
> > > +				.exit_latency		= 1,
> > > +				.target_residency	= 1,
> > > +				.power_usage		= UINT_MAX,
> > > +				.name			= "WFI",
> > > +				.desc			= "ARM WFI",
> > > +			}
> > > +		}
> > > +	};
> > 
> > The stack is gone after the function returns.
> > 
> 
> Argh, I wrongly assumed that cpuidle was actually copying this locally.
> Okay, let's see what else looking clean I can come up with.

I guess you could just use a devm_kzalloc() and then have code similar
to the previous one (data->cpuidle_driver = <template>). You could
alternatively use devm_kmalloc() without zero-initialization but the
advantages of that should be negligible.

Thanks!
Stephan