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Date:   Tue, 12 Dec 2023 11:25:44 +0200 (EET)
From:   =?ISO-8859-15?Q?Ilpo_J=E4rvinen?= <ilpo.jarvinen@linux.intel.com>
To:     Bjorn Helgaas <helgaas@kernel.org>
cc:     Johan Hovold <johan@kernel.org>,
        Johan Hovold <johan+linaro@kernel.org>,
        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        =?ISO-8859-2?Q?Krzysztof_Wilczy=F1ski?= <kw@linux.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Manivannan Sadhasivam <mani@kernel.org>,
        Rob Herring <robh@kernel.org>,
        Nirmal Patel <nirmal.patel@linux.intel.com>,
        Jonathan Derrick <jonathan.derrick@linux.dev>,
        linux-arm-msm@vger.kernel.org, linux-pci@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>, stable@vger.kernel.org,
        Michael Bottini <michael.a.bottini@linux.intel.com>,
        "David E . Box" <david.e.box@linux.intel.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>
Subject: Re: [PATCH v2 1/6] PCI/ASPM: Add locked helper for enabling link
 state
In-Reply-To: <20231208173932.GA798089@bhelgaas>
Message-ID: <f0beb640-5c87-7c8e-64ba-908324347613@linux.intel.com>
References: <20231208173932.GA798089@bhelgaas>
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On Fri, 8 Dec 2023, Bjorn Helgaas wrote:

> On Fri, Dec 08, 2023 at 09:00:56AM +0100, Johan Hovold wrote:
> > On Thu, Dec 07, 2023 at 02:47:16PM -0600, Bjorn Helgaas wrote:
> > > On Tue, Nov 28, 2023 at 09:15:07AM +0100, Johan Hovold wrote:
> > > > Add a helper for enabling link states that can be used in contexts where
> > > > a pci_bus_sem read lock is already held (e.g. from pci_walk_bus()).
> > > > 
> > > > This helper will be used to fix a couple of potential deadlocks where
> > > > the current helper is called with the lock already held, hence the CC
> > > > stable tag.
> > 
> > > As far as I can see, we end up with pci_enable_link_state() defined
> > > but never called and pci_enable_link_state_locked() being called only
> > > by pcie-qcom.c and vmd.c.
> > 
> > Correct, I mentioned this in the cover letter.
> 
> Ah, right.  I really don't like these exported locked/unlocked
> interfaces because pci_bus_sem is internal to the PCI core, and the
> caller shouldn't need to know or be able to specify whether it is held
> or not.  They exist for now, but I think we should try to get rid of
> them.
> 
> > > Can we just rename pci_enable_link_state() to
> > > pci_enable_link_state_locked() and assert that pci_bus_sem is held, so
> > > we don't end up with a function that's never used?
> > 
> > That would work too. I went with adding a new helper to facilitate
> > stable backports and to mirror pci_disable_link_state(). The variants
> > are simple wrappers around the implementation so there's no real cost to
> > having the unused one.
> 
> Makes good sense.  There's no real machine cost to the unused one; I'm
> more concerned about the human cost here.

I know these were already applied but I want to correct one small 
misconcept that seems to be floating around thanks the misleading name...

pci_enable_link_state() is not really a pair/mirror of 
pci_disable_link_state() despite its name. It would be better called
pci_set_default_link_state() to better match what it does.

-- 
 i.