Re: [PATCH v2 3/9] PCI/ASPM: Use RMW accessors for changing LNKCTL

From: Lukas Wunner <lukas@wunner.de>
To: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>
Cc: linux-pci@vger.kernel.org, "Bjorn Helgaas" <bhelgaas@google.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Rob Herring" <robh@kernel.org>,
	"Krzysztof Wilczy??ski" <kw@linux.com>,
	"Emmanuel Grumbach" <emmanuel.grumbach@intel.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"Stefan Mätje" <stefan.maetje@esd.eu>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Jesse Barnes" <jbarnes@virtuousgeek.org>,
	"Matthew Garrett" <mjg59@srcf.ucam.org>,
	"Shaohua Li" <shaohua.li@intel.com>,
	"Thomas Renninger" <trenn@suse.de>,
	"Greg Kroah-Hartman" <gregkh@suse.de>,
	linux-kernel@vger.kernel.org,
	"Dean Luick" <dean.luick@cornelisnetworks.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH v2 3/9] PCI/ASPM: Use RMW accessors for changing LNKCTL
Date: Fri, 16 Jun 2023 21:10:56 +0200	[thread overview]
Message-ID: <20230616191056.GA30821@wunner.de> (raw)
In-Reply-To: <20230517105235.29176-4-ilpo.jarvinen@linux.intel.com>

On Wed, May 17, 2023 at 01:52:29PM +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.
[...]
> @@ -224,17 +223,14 @@ static bool pcie_retrain_link(struct pcie_link_state *link)
>  	if (!pcie_wait_for_retrain(parent))
>  		return false;
>  
> -	pcie_capability_read_word(parent, PCI_EXP_LNKCTL, &reg16);
> -	reg16 |= PCI_EXP_LNKCTL_RL;
> -	pcie_capability_write_word(parent, PCI_EXP_LNKCTL, reg16);
> +	pcie_capability_set_word(parent, PCI_EXP_LNKCTL, PCI_EXP_LNKCTL_RL);
>  	if (parent->clear_retrain_link) {

This and several other RMW operations in drivers/pci/pcie/aspm.c
are touched by commit b1689799772a ("PCI/ASPM: Use distinct local
vars in pcie_retrain_link()") which got applied to pci/enumeration
this week:

https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=enumeration&id=b1689799772a6f4180f918b0ff66e264a3db9796

As a result the $SUBJECT_PATCH no longer applies cleanly and needs
to be respun.

Thanks,

Lukas