linux-kernel - Re: [PATCH] PCI: Enable io space 1k granularity for intel cpu root port

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Date: Fri, 21 Jun 2024 16:02:07 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Zhou Shengqing <zhoushengqing@...info.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Enable io space 1k granularity for intel cpu root
 port

On Fri, Jun 21, 2024 at 02:06:08AM +0000, Zhou Shengqing wrote:
> This patch add 1k granularity for intel root port bridge.Intel latest
> server CPU support 1K granularity,And there is an BIOS setup item named
> "EN1K",but linux doesn't support it. if an IIO has 5 IOU (SPR has 5 IOUs)
> all are bifurcated 2x8.In a 2P server system,There are 20 P2P bridges
> present.if keep 4K granularity allocation,it need 20*4=80k io space,
> exceeding 64k.I test it in a 16*nvidia 4090s system under intel eaglestrem
> platform.There are six 4090s that cannot be allocated I/O resources.
> So I applied this patch.And I found a similar implementation in quirks.c,
> but it only targets the Intel P64H2 platform.
> 
> Signed-off-by: Zhou Shengqing <zhoushengqing@...info.com>
> ---
>  drivers/pci/probe.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 5fbabb4e3425..3f0c901c6653 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -461,6 +461,8 @@ static void pci_read_bridge_windows(struct pci_dev *bridge)
>  	u32 buses;
>  	u16 io;
>  	u32 pmem, tmp;
> +	u16 ven_id, dev_id;
> +	u16 en1k = 0;
>  	struct resource res;
>  
>  	pci_read_config_dword(bridge, PCI_PRIMARY_BUS, &buses);
> @@ -478,6 +480,26 @@ static void pci_read_bridge_windows(struct pci_dev *bridge)
>  	}
>  	if (io) {
>  		bridge->io_window = 1;
> +		if (pci_is_root_bus(bridge->bus)) {
> +			list_for_each_entry(dev, &bridge->bus->devices, bus_list) {
> +				pci_read_config_word(dev, PCI_VENDOR_ID, &ven_id);
> +				pci_read_config_word(dev, PCI_DEVICE_ID, &dev_id);
> +				if (ven_id == PCI_VENDOR_ID_INTEL && dev_id == 0x09a2) {
> +					/*IIO MISC Control offset 0x1c0*/
> +					pci_read_config_word(dev, 0x1c0, &en1k);
> +				}
> +			}
> +		/*
> +		 *Intel ICX SPR EMR GNR
> +		 *IIO MISC Control (IIOMISCCTRL_1_5_0_CFG) — Offset 1C0h
> +		 *bit 2:Enable 1K (EN1K)
> +		 *This bit when set, enables 1K granularity for I/O space decode
> +		 *in each of the virtual P2P bridges
> +		 *corresponding to root ports, and DMI ports.
> +		 */
> +		if (en1k & 0x4)
> +			bridge->io_window_1k = 1;
> +		}

Can you implement this as a quirk similar to quirk_p64h2_1k_io()?

I don't want to clutter the generic code with device-specific things
like this.

>  		pci_read_bridge_io(bridge, &res, true);
>  	}
>  
> -- 
> 2.39.2
>