linux-kernel - Re: [PATCH v3 6/7] PCI: Split up some logic in pcie_bandwidth

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Date:   Thu, 16 Nov 2023 15:02:11 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Mario Limonciello <mario.limonciello@....com>
cc:     Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Lukas Wunner <lukas@...ner.de>,
        Danilo Krummrich <dakr@...hat.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Xinhui Pan <Xinhui.Pan@....com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Pali Rohár <pali@...nel.org>,
        Marek Behún <kabel@...nel.org>,
        "Maciej W . Rozycki" <macro@...am.me.uk>,
        Manivannan Sadhasivam <mani@...nel.org>,
        "open list:DRM DRIVER FOR NVIDIA GEFORCE/QUADRO GPUS" 
        <dri-devel@...ts.freedesktop.org>,
        "open list:DRM DRIVER FOR NVIDIA GEFORCE/QUADRO GPUS" 
        <nouveau@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:RADEON and AMDGPU DRM DRIVERS" 
        <amd-gfx@...ts.freedesktop.org>,
        "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
        "open list:ACPI" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v3 6/7] PCI: Split up some logic in pcie_bandwidth_available()
 to separate function

On Tue, 14 Nov 2023, Mario Limonciello wrote:

> The logic to calculate bandwidth limits may be used at multiple call sites
> so split it up into its own static function instead.
> 
> No intended functional changes.
> 
> Suggested-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
> v2->v3:
>  * Split from previous patch version
> ---
>  drivers/pci/pci.c | 60 +++++++++++++++++++++++++++--------------------
>  1 file changed, 34 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 55bc3576a985..0ff7883cc774 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6224,6 +6224,38 @@ int pcie_set_mps(struct pci_dev *dev, int mps)
>  }
>  EXPORT_SYMBOL(pcie_set_mps);
>  
> +static u32 pcie_calc_bw_limits(struct pci_dev *dev, u32 bw,
> +			       struct pci_dev **limiting_dev,
> +			       enum pci_bus_speed *speed,
> +			       enum pcie_link_width *width)
> +{
> +	enum pcie_link_width next_width;
> +	enum pci_bus_speed next_speed;
> +	u32 next_bw;
> +	u16 lnksta;
> +
> +	pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
> +
> +	next_speed = pcie_link_speed[FIELD_GET(PCI_EXP_LNKSTA_CLS, lnksta)];
> +	next_width = FIELD_GET(PCI_EXP_LNKSTA_NLW, lnksta);
> +
> +	next_bw = next_width * PCIE_SPEED2MBS_ENC(next_speed);
> +
> +	/* Check if current device limits the total bandwidth */

I'd make this a function comment instead and say:

/* Check if @dev limits the total bandwidth. */

Other than that,

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.

> +	if (!bw || next_bw <= bw) {
> +		bw = next_bw;
> +
> +		if (limiting_dev)
> +			*limiting_dev = dev;
> +		if (speed)
> +			*speed = next_speed;
> +		if (width)
> +			*width = next_width;
> +	}
> +
> +	return bw;
> +}
> +
>  /**
>   * pcie_bandwidth_available - determine minimum link settings of a PCIe
>   *			      device and its bandwidth limitation
> @@ -6242,39 +6274,15 @@ u32 pcie_bandwidth_available(struct pci_dev *dev, struct pci_dev **limiting_dev,
>  			     enum pci_bus_speed *speed,
>  			     enum pcie_link_width *width)
>  {
> -	u16 lnksta;
> -	enum pci_bus_speed next_speed;
> -	enum pcie_link_width next_width;
> -	u32 bw, next_bw;
> +	u32 bw = 0;
>  
>  	if (speed)
>  		*speed = PCI_SPEED_UNKNOWN;
>  	if (width)
>  		*width = PCIE_LNK_WIDTH_UNKNOWN;
>  
> -	bw = 0;
> -
>  	while (dev) {
> -		pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
> -
> -		next_speed = pcie_link_speed[FIELD_GET(PCI_EXP_LNKSTA_CLS,
> -						       lnksta)];
> -		next_width = FIELD_GET(PCI_EXP_LNKSTA_NLW, lnksta);
> -
> -		next_bw = next_width * PCIE_SPEED2MBS_ENC(next_speed);
> -
> -		/* Check if current device limits the total bandwidth */
> -		if (!bw || next_bw <= bw) {
> -			bw = next_bw;
> -
> -			if (limiting_dev)
> -				*limiting_dev = dev;
> -			if (speed)
> -				*speed = next_speed;
> -			if (width)
> -				*width = next_width;
> -		}
> -
> +		bw = pcie_calc_bw_limits(dev, bw, limiting_dev, speed, width);
>  		dev = pci_upstream_bridge(dev);
>  	}
>  
>