From: Bjorn Helgaas <helgaas@kernel.org>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
"Andrew Murray" <amurray@thegoodpenguin.co.uk>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Marek Behún" <marek.behun@nic.cz>,
"Remi Pommarel" <repk@triplefau.lt>,
"Tomasz Maciej Nowak" <tmn505@gmail.com>,
Xogium <contact@xogium.me>,
linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PCI: aardvark: Don't touch PCIe registers if no card connected
Date: Thu, 28 May 2020 11:49:38 -0500 [thread overview]
Message-ID: <20200528164938.GA325239@bjorn-Precision-5520> (raw)
In-Reply-To: <20200528163809.54f5ldvphrjg3zg3@pali>
On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote:
> On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote:
> > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote:
> > > When there is no PCIe card connected and advk_pcie_rd_conf() or
> > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated
> > > root bridge, the aardvark driver throws the following error message:
> > >
> > > advk-pcie d0070000.pcie: config read/write timed out
> > >
> > > Obviously accessing PCIe registers of disconnected card is not possible.
> > >
> > > Extend check in advk_pcie_valid_device() function for validating
> > > availability of PCIe bus. If PCIe link is down, then the device is marked
> > > as Not Found and the driver does not try to access these registers.
> > >
> > > Signed-off-by: Pali Rohár <pali@kernel.org>
> > > ---
> > > drivers/pci/controller/pci-aardvark.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > index 90ff291c24f0..53a4cfd7d377 100644
> > > --- a/drivers/pci/controller/pci-aardvark.c
> > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus,
> > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0)
> > > return false;
> > >
> > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie))
> > > + return false;
> >
> > I don't think this is the right fix. This makes it racy because the
> > link may go down after we call advk_pcie_valid_device() but before we
> > perform the config read.
>
> Yes, it is racy, but I do not think it cause problems. Trying to read
> PCIe registers when device is not connected cause just those timeouts,
> printing error message and increased delay in advk_pcie_wait_pio() due
> to polling loop. This patch reduce unnecessary access to PCIe registers
> when advk_pcie_wait_pio() polling just fail.
>
> I think it is a good idea to not call blocking advk_pcie_wait_pio() when
> it is not needed. We could have faster enumeration of PCIe buses when
> card is not connected.
Maybe advk_pcie_check_pio_status() and advk_pcie_wait_pio() could be
combined so we could get the correct error status as soon as it's
available, without waiting for a timeout?
In any event, the "return PCIBIOS_SET_FAILED" needs to be fixed. Most
callers of config read do not check for failure, but most of the ones
that do, check for "val == ~0". Only a few check for a status of
other than PCIBIOS_SUCCESSFUL.
> > I have no objection to removing the "config read/write timed out"
> > message. The "return PCIBIOS_SET_FAILED" in the read case probably
> > should be augmented by setting "*val = 0xffffffff".
> >
> > > return true;
> > > }
> > >
> > > --
> > > 2.20.1
> > >
next prev parent reply other threads:[~2020-05-28 16:49 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 14:31 [PATCH] PCI: aardvark: Don't touch PCIe registers if no card connected Pali Rohár
2020-05-28 16:26 ` Bjorn Helgaas
2020-05-28 16:38 ` Pali Rohár
2020-05-28 16:49 ` Bjorn Helgaas [this message]
2020-05-29 8:30 ` Pali Rohár
2020-06-30 12:31 ` Pali Rohár
2020-06-30 13:51 ` Bjorn Helgaas
2020-06-30 14:04 ` Pali Rohár
2020-06-30 14:58 ` Bjorn Helgaas
2020-07-01 8:08 ` Pali Rohár
2020-07-01 8:20 ` [PATCH v2] " Pali Rohár
2020-07-01 21:34 ` Bjorn Helgaas
2020-07-02 8:23 ` Pali Rohár
2020-07-02 8:30 ` [PATCH v3] " Pali Rohár
2020-07-09 11:35 ` Lorenzo Pieralisi
2020-07-09 12:22 ` Pali Rohár
2020-07-09 14:47 ` Lorenzo Pieralisi
2020-07-09 15:09 ` Pali Rohár
2020-07-10 9:18 ` Lorenzo Pieralisi
2020-07-10 15:44 ` Pali Rohár
2020-07-10 16:08 ` Bjorn Helgaas
2020-07-10 19:30 ` Pali Rohár
2020-07-10 20:08 ` Bjorn Helgaas
2020-07-13 8:27 ` Pali Rohár
2020-07-13 11:23 ` Lorenzo Pieralisi
2020-07-13 14:50 ` Pali Rohár
2020-07-13 16:41 ` Lorenzo Pieralisi
2020-07-14 7:38 ` Pali Rohár
2020-07-15 12:17 ` Pali Rohár
2020-07-15 16:21 ` Lorenzo Pieralisi
2020-07-21 8:57 ` Pali Rohár
2020-07-21 10:48 ` Lorenzo Pieralisi
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