linux-kernel - Re: [PATCH v3] PCI: Add quirk for preventing bus reset on TI C667X

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Message-ID: <20210312210917.GA2290948@bjorn-Precision-5520>
Date:   Fri, 12 Mar 2021 15:09:17 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Antti Järvinen <antti.jarvinen@...il.com>
Cc:     kw@...ux.com, alex.williamson@...hat.com, bhelgaas@...gle.com,
        kishon@...com, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, m-karicheri2@...com
Subject: Re: [PATCH v3] PCI: Add quirk for preventing bus reset on TI C667X

On Mon, Mar 08, 2021 at 02:21:30PM +0000, Antti Järvinen wrote:
> Some TI KeyStone C667X devices do no support bus/hot reset. Its PCIESS
> automatically disables LTSSM when secondary bus reset is received and
> device stops working. Prevent bus reset by adding quirk_no_bus_reset to
> the device. With this change device can be assigned to VMs with VFIO,
> but it will leak state between VMs.

s/do no/do/not/ (also in the comment below)

Does the user get any indication of this leaking state?  I looked
through drivers/vfio and drivers/pci, but I haven't found anything
yet.

We *could* log something in quirk_no_bus_reset(), but that would just
be noise for people who don't pass the device through to a VM.  So
maybe it would be nicer if we logged something when we actually *do*
pass it through to a VM.

> Reference: https://e2e.ti.com/support/processors/f/791/t/954382
> Signed-off-by: Antti Järvinen <antti.jarvinen@...il.com>
> ---
>  drivers/pci/quirks.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 653660e3ba9e..d9201ad1ca39 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -3578,6 +3578,16 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0034, quirk_no_bus_reset);
>   */
>  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_CAVIUM, 0xa100, quirk_no_bus_reset);
>  
> +/*
> + * Some TI keystone C667X devices do no support bus/hot reset.
> + * Its PCIESS automatically disables LTSSM when secondary bus reset is
> + * received and device stops working. Prevent bus reset by adding
> + * quirk_no_bus_reset to the device. With this change device can be
> + * assigned to VMs with VFIO, but it will leak state between VMs.
> + * Reference https://e2e.ti.com/support/processors/f/791/t/954382
> + */
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_TI, 0xb005, quirk_no_bus_reset);
> +
>  static void quirk_no_pm_reset(struct pci_dev *dev)
>  {
>  	/*
> -- 
> 2.17.1
>