linux-kernel - Re: [PATCH v4 3/4] PCI: dwc: Reduce DT reads by allocating host bridge via DWC glue driver

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Message-ID: <20250210092010.nyt3n3tflipcrpt2@thinkpad>
Date: Mon, 10 Feb 2025 14:50:10 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: cros-qcom-dts-watchers@...omium.org,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jingoo Han <jingoohan1@...il.com>, linux-arm-msm@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, quic_vbadigan@...cinc.com,
	quic_mrana@...cinc.com, quic_vpernami@...cinc.com,
	mmareddy@...cinc.com
Subject: Re: [PATCH v4 3/4] PCI: dwc: Reduce DT reads by allocating host
 bridge via DWC glue driver

On Fri, Feb 07, 2025 at 04:58:58AM +0530, Krishna Chaitanya Chundru wrote:
> dw_pcie_ecam_supported() needs to read bus-range to find the maximum
> bus range value. The devm_pci_alloc_host_bridge() is already reading
> bus range and storing it in host bridge.If devm_pci_alloc_host_bridge()

What do you mean by 'storig in host bridge' here? Mention the exact structure
name if that's what you are referring to.

> moved to start of the controller probe, the dt reading can be avoided
> and use values stored in the host bridge.

Same here.

> 
> Allow DWC glue drivers to allocate the host bridge, avoiding redundant
> device tree reads primarily in dw_pcie_ecam_supported().
> 

This makes little sense to me. By this change, you essentially want DWC glue
drivers to call devm_pci_alloc_host_bridge() just to get rid of one range
parsing.

I'd suggest to move dw_pcie_ecam_supported() inside dw_pcie_host_init() and call
after devm_pci_alloc_host_bridge(). This way, the glue drivers can rely on DWC
core to detect ECAM like other resources. And the API could be renamed as
dw_pcie_ecam_detect() to match other resource detection like iATU, eDMA.

More in patch 4.

- Mani

> Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 826ff9338646..a18cb1e411e4 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -484,8 +484,8 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>  	struct device *dev = pci->dev;
>  	struct device_node *np = dev->of_node;
>  	struct platform_device *pdev = to_platform_device(dev);
> +	struct pci_host_bridge *bridge = pp->bridge;
>  	struct resource_entry *win;
> -	struct pci_host_bridge *bridge;
>  	struct resource *res;
>  	int ret;
>  
> @@ -527,7 +527,12 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>  	if (!bridge)
>  		return -ENOMEM;
>  
> -	pp->bridge = bridge;
> +	if (!pp->bridge) {
> +		bridge = devm_pci_alloc_host_bridge(dev, 0);
> +		if (!bridge)
> +			return -ENOMEM;
> +		pp->bridge = bridge;
> +	}
>  
>  	/* Get the I/O range from DT */
>  	win = resource_list_first_type(&bridge->windows, IORESOURCE_IO);
> 
> -- 
> 2.34.1
> 

-- 
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