linux-kernel - Re: [PATCH V3 1/1] Intel Sky Lake-E host root ports check.

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Date:   Tue, 29 Mar 2022 20:42:19 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Shlomo Pongratz <shlomopongratz@...il.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        andrew.maier@...eticom.com, logang@...tatee.com,
        bhelgaas@...gle.com, Shlomo Pongratz <shlomop@...ops.com>
Subject: Re: [PATCH V3 1/1] Intel Sky Lake-E host root ports check.

On Tue, Mar 29, 2022 at 01:43:21PM +0300, Shlomo Pongratz wrote:
> On commit 7b94b53db34f ("PCI/P2PDMA: Add Intel Sky Lake-E Root Ports B, C, D to the whitelist")

'in commit' and it is expected to word wrap the description

> Andrew Maier added the Sky Lake-E additional devices
> 2031, 2032 and 2033 root ports to the already existing 2030 device.
> 
> The Intel devices 2030, 2031, 2032 and 2033 which are ports A, B, C and D,
> and if all exist they will occupy slots 0 till 3 in that order.
> 
> Now if for example device 2030 is missing then there will no device on slot 0, but
> other devices can reside on other slots according to there port.
> For this reason the test that insisted that the bridge should be on slot 0 was modified
> to support bridges that are not on slot 0.

This needs updating to the new test

> 
> Signed-off-by: Shlomo Pongratz <shlomop@...ops.com>
>  drivers/pci/p2pdma.c | 42 +++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 37 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 30b1df3c9d2f..c088d4ab64f4 100644
> +++ b/drivers/pci/p2pdma.c
> @@ -307,6 +307,7 @@ static const struct pci_p2pdma_whitelist_entry {
>  	unsigned short device;
>  	enum {
>  		REQ_SAME_HOST_BRIDGE	= 1 << 0,
> +		IS_ROOT_PORT		= 1 << 1,
>  	} flags;
>  } pci_p2pdma_whitelist[] = {
>  	/* Intel Xeon E5/Core i7 */
> @@ -316,15 +317,38 @@ static const struct pci_p2pdma_whitelist_entry {
>  	{PCI_VENDOR_ID_INTEL,	0x2f00, REQ_SAME_HOST_BRIDGE},
>  	{PCI_VENDOR_ID_INTEL,	0x2f01, REQ_SAME_HOST_BRIDGE},
>  	/* Intel SkyLake-E */
> -	{PCI_VENDOR_ID_INTEL,	0x2030, 0},
> -	{PCI_VENDOR_ID_INTEL,	0x2031, 0},
> -	{PCI_VENDOR_ID_INTEL,	0x2032, 0},
> -	{PCI_VENDOR_ID_INTEL,	0x2033, 0},
> +	{PCI_VENDOR_ID_INTEL,	0x2030, IS_ROOT_PORT},
> +	{PCI_VENDOR_ID_INTEL,	0x2031, IS_ROOT_PORT},
> +	{PCI_VENDOR_ID_INTEL,	0x2032, IS_ROOT_PORT},
> +	{PCI_VENDOR_ID_INTEL,	0x2033, IS_ROOT_PORT},
>  	{PCI_VENDOR_ID_INTEL,	0x2020, 0},
>  	{PCI_VENDOR_ID_INTEL,	0x09a2, 0},
>  	{}
>  };
>  
> +/*
> + * The functionality of thisunction can be integrated into
> + * __host_bridge_whitelist function but this will make the code
> + * less readable

This comment is not useful, explain what the function does or delete
it

> + */
> +static bool pci_is_root_port(struct pci_dev *root)
> +{
> +	const struct pci_p2pdma_whitelist_entry *entry;
> +	unsigned short vendor, device;
> +
> +	vendor = root->vendor;
> +	device = root->device;
> +
> +	for (entry = pci_p2pdma_whitelist; entry->vendor; entry++) {
> +		if (vendor != entry->vendor || device != entry->device)
> +			continue;
> +
> +		if (entry->flags & IS_ROOT_PORT)
> +			return true;
> +	}
> +	return false;
> +}
> +
>  /*
>   * This lookup function tries to find the PCI device corresponding to a given
>   * host bridge.
> @@ -333,6 +357,11 @@ static const struct pci_p2pdma_whitelist_entry {
>   * bus->devices list and that the devfn is 00.0. These assumptions should hold
>   * for all the devices in the whitelist above.
>   *
> + * The method above will work in most cases but not for all.
> + * Note that the Intel devices 2030, 2031, 2032 and 2033 are ports A, B, C and D.
> + * Consider on a bus X only port C has devices connected to it so in the PCI scan only
> + * device 8086:2032 on 0000:X:02.0 will be found as bridges with no children are ignored
> + *
>   * 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.
> @@ -350,7 +379,9 @@ static struct pci_dev *pci_host_bridge_dev(struct pci_host_bridge *host)
>  
>  	if (!root)
>  		return NULL;
> -	if (root->devfn != PCI_DEVFN(0, 0))
> +
> +	/* Intel Sky Lake-E host root ports can be on no zero slot */
> +	if (root->devfn != PCI_DEVFN(0, 0) && !pci_is_root_port(root))
>  		return NULL;

The name pci_host_bridge_dev needs some attention if it is now
returning a root port.

> @@ -372,6 +403,7 @@ static bool __host_bridge_whitelist(struct pci_host_bridge *host,
>  	for (entry = pci_p2pdma_whitelist; entry->vendor; entry++) {
>  		if (vendor != entry->vendor || device != entry->device)
>  			continue;
> +
>  		if (entry->flags & REQ_SAME_HOST_BRIDGE && !same_host_bridge)
>  			return false;

Unnecessary hunk

Jason