linux-kernel - Re: [PATCHv5 16/20] PCI: mobiveil: Add link up condition check

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Message-ID: <20190611171733.GB22836@redmoon>
Date:   Tue, 11 Jun 2019 18:17:33 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     "Z.q. Hou" <zhiqiang.hou@....com>, bhelgaas@...gle.com
Cc:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "l.subrahmanya@...iveil.co.in" <l.subrahmanya@...iveil.co.in>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        Mingkai Hu <mingkai.hu@....com>,
        "M.h. Lian" <minghuan.lian@....com>,
        Xiaowei Bao <xiaowei.bao@....com>
Subject: Re: [PATCHv5 16/20] PCI: mobiveil: Add link up condition check

NB: Please trim the CC list and keep it to concerned maintainers.

On Fri, Apr 12, 2019 at 08:36:48AM +0000, Z.q. Hou wrote:
> From: Hou Zhiqiang <Zhiqiang.Hou@....com>
> 
> Avoid to issue CFG transactions to link partner when the PCIe
> link is not up.
> 
> Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@....com>
> ---
> V5:
>  - Corrected the subject.
> 
>  drivers/pci/controller/pcie-mobiveil.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/controller/pcie-mobiveil.c b/drivers/pci/controller/pcie-mobiveil.c
> index 621852078caf..1ee3ea2570c0 100644
> --- a/drivers/pci/controller/pcie-mobiveil.c
> +++ b/drivers/pci/controller/pcie-mobiveil.c
> @@ -283,6 +283,10 @@ static bool mobiveil_pcie_valid_device(struct pci_bus *bus, unsigned int devfn)
>  {
>  	struct mobiveil_pcie *pcie = bus->sysdata;
>  
> +	/* If there is no link, then there is no device */
> +	if (bus->number > pcie->root_bus_nr && !mobiveil_pcie_link_up(pcie))

I think Bjorn mentioned this a million times already, eg:

https://lore.kernel.org/linux-pci/20190411201535.GS256045@google.com/

this is racy and gives a false sense of robustness. We have code in the
kernel that checks the link but adding more seems silly to me, so I am
inclined to drop this patch.

Lorenzo

> +		return false;
> +
>  	/* Only one device down on each root port */
>  	if ((bus->number == pcie->root_bus_nr) && (devfn > 0))
>  		return false;
> -- 
> 2.17.1
>