linux-kernel - Re: [PATCH V7 1/1] Intel Sky Lake-E host root ports check.

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Date:   Mon, 11 Apr 2022 17:03:55 +0300
From:   Maor Gottlieb <maorg@...dia.com>
To:     Shlomo Pongratz <shlomopongratz@...il.com>,
        <linux-pci@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <andrew.maier@...eticom.com>,
        <logang@...tatee.com>, <bhelgaas@...gle.com>, <jgg@...dia.com>,
        <helgaas@...nel.org>, Shlomo Pongratz <shlomop@...ops.com>
Subject: Re: [PATCH V7 1/1] Intel Sky Lake-E host root ports check.


> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 30b1df3c9d2f..187047be83a0 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -327,15 +327,19 @@ static const struct pci_p2pdma_whitelist_entry {
>   
>   /*
>    * This lookup function tries to find the PCI device corresponding to a given
> - * host bridge.
> + * host bridge or a root port.
>    *
>    * It assumes the host bridge device is the first PCI device in the
> - * bus->devices list and that the devfn is 00.0. These assumptions should hold
> - * for all the devices in the whitelist above.
> + * bus->devices list and that the devfn is 00.0. The first assumption should
> + * hold for all the devices in the whitelist above, however the second
> + * assumption doesn't always hold for root ports.
> + * For example for Intel Skylake devices 2030, 2031, 2032 and 2033,
> + * which are root ports (A, B, C and D respectively).
> + * So the function checks explicitly that the device is a root port.
>    *
> - * This function is equivalent to pci_get_slot(host->bus, 0), however it does
> - * not take the pci_bus_sem lock seeing __host_bridge_whitelist() must not
> - * sleep.
> + * This function is equivalent to pci_get_slot(host->bus, 0) (except for
> + * the root port test), however it does not take the pci_bus_sem lock seeing
> + * __host_bridge_whitelist() must not sleep.
>    *
>    * For this to be safe, the caller should hold a reference to a device on the
>    * bridge, which should ensure the host_bridge device will not be freed
> @@ -350,10 +354,19 @@ static struct pci_dev *pci_host_bridge_dev(struct pci_host_bridge *host)
>   
>   	if (!root)
>   		return NULL;
> -	if (root->devfn != PCI_DEVFN(0, 0))
> -		return NULL;
>   
> -	return root;
> +	/* Verify that the device is a host bridge or a root port
> +	 * It is assumed that host bridges have a 0 devfn, (common practice)
> +	 * but some of the entries in the whitelist are root ports that can
> +	 * have any devfn
> +	 */
> +	if (root->devfn == PCI_DEVFN(0, 0))
> +		return root;
> +
> +	if (pci_pcie_type(root) == PCI_EXP_TYPE_ROOT_PORT)
> +		return root;
> +
> +	return NULL;
>   }
>   
>   static bool __host_bridge_whitelist(struct pci_host_bridge *host,

Thanks, it also helped our system.

Tested-by: Maor Gottlieb <maorg@...dia.com>