linux-kernel - Re: [PATCH] PCI: aardvark: Don't touch PCIe registers if no card connected

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Message-ID: <20200528162604.GA323482@bjorn-Precision-5520>
Date:   Thu, 28 May 2020 11:26:04 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Andrew Murray <amurray@...goodpenguin.co.uk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Marek Behún <marek.behun@....cz>,
        Remi Pommarel <repk@...plefau.lt>,
        Tomasz Maciej Nowak <tmn505@...il.com>,
        Xogium <contact@...ium.me>, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: aardvark: Don't touch PCIe registers if no card
 connected

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@...nel.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.

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
>