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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: Tue, 30 Jun 2020 08:51:27 -0500	[thread overview]
Message-ID: <20200630135127.GA3414186@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.

What happens when the device is removed after advk_pcie_link_up()
returns true, but before we actually do the config access?

WARNING: multiple messages have this Message-ID
From: Bjorn Helgaas <helgaas@kernel.org>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Tomasz Maciej Nowak" <tmn505@gmail.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	linux-pci@vger.kernel.org, Xogium <contact@xogium.me>,
	linux-kernel@vger.kernel.org, "Marek Behún" <marek.behun@nic.cz>,
	"Remi Pommarel" <repk@triplefau.lt>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	linux-arm-kernel@lists.infradead.org,
	"Andrew Murray" <amurray@thegoodpenguin.co.uk>
Subject: Re: [PATCH] PCI: aardvark: Don't touch PCIe registers if no card connected
Date: Tue, 30 Jun 2020 08:51:27 -0500	[thread overview]
Message-ID: <20200630135127.GA3414186@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.

What happens when the device is removed after advk_pcie_link_up()
returns true, but before we actually do the config access?

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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2020-06-30 13:53 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-28 14:31 Pali Rohár
2020-05-28 14:31 ` Pali Rohár
2020-05-28 16:26 ` Bjorn Helgaas
2020-05-28 16:26   ` Bjorn Helgaas
2020-05-28 16:38   ` Pali Rohár
2020-05-28 16:38     ` Pali Rohár
2020-05-28 16:49     ` Bjorn Helgaas
2020-05-28 16:49       ` Bjorn Helgaas
2020-05-29  8:30       ` Pali Rohár
2020-05-29  8:30         ` Pali Rohár
2020-06-30 12:31         ` Pali Rohár
2020-06-30 12:31           ` Pali Rohár
2020-06-30 13:51     ` Bjorn Helgaas [this message]
2020-06-30 13:51       ` Bjorn Helgaas
2020-06-30 14:04       ` Pali Rohár
2020-06-30 14:04         ` Pali Rohár
2020-06-30 14:58         ` Bjorn Helgaas
2020-06-30 14:58           ` Bjorn Helgaas
2020-07-01  8:08           ` Pali Rohár
2020-07-01  8:08             ` Pali Rohár
2020-07-01  8:20 ` [PATCH v2] " Pali Rohár
2020-07-01  8:20   ` Pali Rohár
2020-07-01 21:34   ` Bjorn Helgaas
2020-07-01 21:34     ` Bjorn Helgaas
2020-07-02  8:23     ` Pali Rohár
2020-07-02  8:23       ` Pali Rohár
2020-07-02  8:30 ` [PATCH v3] " Pali Rohár
2020-07-02  8:30   ` Pali Rohár
2020-07-09 11:35   ` Lorenzo Pieralisi
2020-07-09 11:35     ` Lorenzo Pieralisi
2020-07-09 12:22     ` Pali Rohár
2020-07-09 12:22       ` Pali Rohár
2020-07-09 14:47       ` Lorenzo Pieralisi
2020-07-09 14:47         ` Lorenzo Pieralisi
2020-07-09 15:09         ` Pali Rohár
2020-07-09 15:09           ` Pali Rohár
2020-07-10  9:18           ` Lorenzo Pieralisi
2020-07-10  9:18             ` Lorenzo Pieralisi
2020-07-10 15:44             ` Pali Rohár
2020-07-10 15:44               ` Pali Rohár
2020-07-10 16:08               ` Bjorn Helgaas
2020-07-10 16:08                 ` Bjorn Helgaas
2020-07-10 19:30                 ` Pali Rohár
2020-07-10 19:30                   ` Pali Rohár
2020-07-10 20:08                   ` Bjorn Helgaas
2020-07-10 20:08                     ` Bjorn Helgaas
2020-07-13  8:27             ` Pali Rohár
2020-07-13  8:27               ` Pali Rohár
2020-07-13 11:23               ` Lorenzo Pieralisi
2020-07-13 11:23                 ` Lorenzo Pieralisi
2020-07-13 14:50                 ` Pali Rohár
2020-07-13 14:50                   ` Pali Rohár
2020-07-13 16:41                   ` Lorenzo Pieralisi
2020-07-13 16:41                     ` Lorenzo Pieralisi
2020-07-14  7:38                     ` Pali Rohár
2020-07-14  7:38                       ` Pali Rohár
2020-07-15 12:17                 ` Pali Rohár
2020-07-15 12:17                   ` Pali Rohár
2020-07-15 16:21                   ` Lorenzo Pieralisi
2020-07-15 16:21                     ` Lorenzo Pieralisi
2020-07-21  8:57                     ` Pali Rohár
2020-07-21  8:57                       ` Pali Rohár
2020-07-21 10:48                       ` Lorenzo Pieralisi
2020-07-21 10:48                         ` Lorenzo Pieralisi

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