linux-kernel - Re: [PATCH v3 1/3] PCI: Configure root port MPS during host probing

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Message-ID: <aBsN2_YG0RsH4RPA@ryzen>
Date: Wed, 7 May 2025 09:38:03 +0200
From: Niklas Cassel <cassel@...nel.org>
To: Hans Zhang <18255117159@....com>
Cc: lpieralisi@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
	heiko@...ech.de, manivannan.sadhasivam@...aro.org,
	yue.wang@...ogic.com, pali@...nel.org, neil.armstrong@...aro.org,
	robh@...nel.org, jingoohan1@...il.com, khilman@...libre.com,
	jbrunet@...libre.com, martin.blumenstingl@...glemail.com,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-amlogic@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v3 1/3] PCI: Configure root port MPS during host probing

On Wed, May 07, 2025 at 01:34:37AM +0800, Hans Zhang wrote:

(snip)

>  static void pci_configure_mps(struct pci_dev *dev)
>  {
>  	struct pci_dev *bridge = pci_upstream_bridge(dev);
> @@ -2178,6 +2209,10 @@ static void pci_configure_mps(struct pci_dev *dev)
>  		return;
>  	}

We should probably add a comment explaining why we are doing this here.

Perhaps something like:

/*
 * Unless MPS strategy is PCIE_BUS_TUNE_OFF (don't touch MPS at all),
 * start off by setting root ports' MPS to MPSS. Depending on the MPS
 * strategy, and the MPSS of the devices below the root port, the MPS
 * of the root port might get overriden later.
 */


> +	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT &&
> +	    pcie_bus_config != PCIE_BUS_TUNE_OFF)
> +		pcie_write_mps(dev, 128 << dev->pcie_mpss);
> +
>  	if (!bridge || !pci_is_pcie(bridge))
>  		return;
>  


Kind regards,
Niklas