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

[Manivannan Sadhasivam]

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@xxxxxxxxxx>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
> ---
>  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
> 

-- 
மணிவண்ணன் சதாசிவம்