linux-kernel - Re: [PATCH v2 2/2] PCI: qcom: Enable ASPM for platforms supporting 1.9.0 ops

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Date:   Wed, 11 Oct 2023 10:33:39 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        lpieralisi@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
        robh@...nel.org, gustavo.pimentel@...opsys.com,
        jingoohan1@...il.com, andersson@...nel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 2/2] PCI: qcom: Enable ASPM for platforms supporting
 1.9.0 ops

On Tue, Oct 10, 2023 at 06:33:52PM +0200, Konrad Dybcio wrote:
> 
> 
> On 10/10/23 17:59, Manivannan Sadhasivam wrote:
> > ASPM is supported by Qcom host controllers/bridges on most of the recent
> > platforms and so the devices tested so far. But for enabling ASPM by
> > default (without Kconfig/cmdline/sysfs), BIOS has to enable ASPM on both
> > host bridge and downstream devices during boot. Unfortunately, none of the
> > BIOS available on Qcom platforms enables ASPM. Due to this, the platforms
> > making use of Qcom SoCs draw high power during runtime.
> > 
> > To fix this power issue, users/distros have to enable ASPM using configs
> > such as (Kconfig/cmdline/sysfs) or the BIOS has to start enabling ASPM.
> > The latter may happen in the future, but that won't address the issue on
> > current platforms. Also, asking users/distros to enable a feature to get
> > the power management right would provide an unpleasant out-of-the-box
> > experience.
> > 
> > So the apt solution is to enable ASPM in the controller driver itself. And
> > this is being accomplished by calling pci_enable_link_state() in the newly
> > introduced host_post_init() callback for all the devices connected to the
> > bus. This function enables all supported link low power states for both
> > host bridge and the downstream devices.
> > 
> > Due to limited testing, ASPM is only enabled for platforms making use of
> > ops_1_9_0 callbacks.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> [...]
> 
> > +static int qcom_pcie_enable_aspm(struct pci_dev *pdev, void *userdata)
> > +{
> > +	/* Downstream devices need to be in D0 state before enabling PCI PM substates */
> > +	pci_set_power_state(pdev, PCI_D0);
> > +	pci_enable_link_state(pdev, PCIE_LINK_STATE_ALL);
> Do we not care about retval here?
> 

No. Even if it fails, we shouldn't care about it.

> > +
> > +	return 0;
> > +}
> > +
> > +static void qcom_pcie_host_post_init_2_7_0(struct qcom_pcie *pcie)
> post_init_enable_aspm?
> 

The scope of this callback may get extended in the future. So I'd keep it as it
is.

- Mani

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