From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Thomas Petazzoni" <thomas.petazzoni@bootlin.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 v3] PCI: aardvark: Don't touch PCIe registers if no card connected
Date: Thu, 9 Jul 2020 12:35:09 +0100 [thread overview]
Message-ID: <20200709113509.GB19638@e121166-lin.cambridge.arm.com> (raw)
In-Reply-To: <20200702083036.12230-1-pali@kernel.org>
On Thu, Jul 02, 2020 at 10:30:36AM +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.
>
> This is just an optimization to prevent accessing PCIe registers when card
> is disconnected. Trying to access PCIe registers of disconnected card does
> not cause any crash, kernel just needs to wait for a timeout. So if card
> disappear immediately after checking for PCIe link (before accessing PCIe
> registers), it does not cause any problems.
>
> Signed-off-by: Pali Rohár <pali@kernel.org>
>
> ---
> Changes in V3:
> * Add comment to the code
> Changes in V2:
> * Update commit message, mention that this is optimization
> ---
> drivers/pci/controller/pci-aardvark.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 90ff291c24f0..d18f389b36a1 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -644,6 +644,13 @@ 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 the link goes down after we check for link-up, nothing bad
> + * happens but the config access times out.
> + */
> + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie))
> + return false;
> +
> return true;
> }
Question: this basically means that you can only effectively enumerate
bus number == root_bus_nr and AFAICS if at probe the link did not
come up it will never do, will it ?
Isn't this equivalent to limiting the bus numbers the bridge is capable
of handling ?
Reworded: if in advk_pcie_setup_hw() the link does not come up, what's
the point of trying to enumerate the bus hierarchy below the root bus ?
Thanks,
Lorenzo
next prev parent reply other threads:[~2020-07-09 11:35 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
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 [this message]
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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