linux-kernel - Re: [PATCH v4 04/11] PCI/ASPM: Use RMW accessors for changing LNKCTL

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Message-ID: <ZLEP+FPwsvk8jw5E@smile.fi.intel.com>
Date:   Fri, 14 Jul 2023 12:06:00 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Lukas Wunner <lukas@...ner.de>,
        Jesse Barnes <jbarnes@...tuousgeek.org>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Shaohua Li <shaohua.li@...el.com>,
        Thomas Renninger <trenn@...e.de>,
        Greg Kroah-Hartman <gregkh@...e.de>,
        linux-kernel@...r.kernel.org,
        Dean Luick <dean.luick@...nelisnetworks.com>,
        Jonas Dreßler <verdre@...d.nl>,
        stable@...r.kernel.org
Subject: Re: [PATCH v4 04/11] PCI/ASPM: Use RMW accessors for changing LNKCTL

On Thu, Jul 13, 2023 at 03:44:58PM +0300, Ilpo Järvinen wrote:
> Don't assume that the device is fully under the control of ASPM and use
> RMW capability accessors which do proper locking to avoid losing
> concurrent updates to the register values.
> 
> If configuration fails in pcie_aspm_configure_common_clock(), the
> function attempts to restore the old PCI_EXP_LNKCTL_CCC settings. Store
> only the old PCI_EXP_LNKCTL_CCC bit for the relevant devices rather
> than the content of the whole LNKCTL registers. It aligns better with
> how pcie_lnkctl_clear_and_set() expects its parameter and makes the
> code more obvious to understand.

...

>  	int same_clock = 1;
> -	u16 reg16, parent_reg, child_reg[8];
> +	u16 reg16, parent_old_ccc, child_old_ccc[8];

	u16 ccc;

>  	struct pci_dev *child, *parent = link->pdev;
>  	struct pci_bus *linkbus = parent->subordinate;

...

	ccc = same_clock ? PCI_EXP_LNKCTL_CCC : 0);

>  	/* Configure downstream component, all functions */
>  	list_for_each_entry(child, &linkbus->devices, bus_list) {
>  		pcie_capability_read_word(child, PCI_EXP_LNKCTL, &reg16);
> -		child_reg[PCI_FUNC(child->devfn)] = reg16;
> -		if (same_clock)
> -			reg16 |= PCI_EXP_LNKCTL_CCC;
> -		else
> -			reg16 &= ~PCI_EXP_LNKCTL_CCC;
> -		pcie_capability_write_word(child, PCI_EXP_LNKCTL, reg16);
> +		child_old_ccc[PCI_FUNC(child->devfn)] = reg16 & PCI_EXP_LNKCTL_CCC;
> +		pcie_capability_clear_and_set_word(child, PCI_EXP_LNKCTL,
> +						   PCI_EXP_LNKCTL_CCC,
> +						   same_clock ? PCI_EXP_LNKCTL_CCC : 0);

		pcie_capability_clear_and_set_word(child, PCI_EXP_LNKCTL,
						   PCI_EXP_LNKCTL_CCC, ccc);

>  	}

...

> +	pcie_capability_clear_and_set_word(parent, PCI_EXP_LNKCTL,
> +					   PCI_EXP_LNKCTL_CCC,
> +					   same_clock ? PCI_EXP_LNKCTL_CCC : 0);

	pcie_capability_clear_and_set_word(parent, PCI_EXP_LNKCTL,
					   PCI_EXP_LNKCTL_CCC, ccc);

?

-- 
With Best Regards,
Andy Shevchenko