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

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Date:   Mon, 19 Jun 2023 19:06:51 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
cc:     Lukas Wunner <lukas@...ner.de>, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczy??ski <kw@...ux.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Stefan Mätje <stefan.maetje@....eu>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        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>,
        LKML <linux-kernel@...r.kernel.org>,
        Dean Luick <dean.luick@...nelisnetworks.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 3/9] PCI/ASPM: Use RMW accessors for changing LNKCTL

On Mon, 19 Jun 2023, Bjorn Helgaas wrote:

> On Mon, Jun 19, 2023 at 05:45:06PM +0300, Ilpo Järvinen wrote:
> > On Fri, 16 Jun 2023, Lukas Wunner wrote:
> > > 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.
> > 
> > Okay but I'm a bit lost which commit/head in pci repo I should now base 
> > this series because there's a conflict between pci/aspm and 
> > pci/enumeration which is not resolved in the repo because pci/enumeration 
> > hasn't advanced into pci/next yet. Any suggestion?
> 
> Generally speaking I prefer patches based on the PCI "main" branch
> (usually -rc1) because I base topic branches on that.  If there are
> conflicts with other pending material, it's great if you can mention
> them, but I can resolve them when applying, so no need to repost just
> for that.

Just to confirm I'm understanding this correctly... Am I supposed to send
a patch whose changelog description and diff do not agree?? (The diff 
will still modify pcie/aspm.c if it's main-based and the description 
refers to something more generic as per Lukas' request since the code got 
moved into pci.c in the enumeration branch).


-- 
 i.