Re: [PATCH v3 3/4] PCI: dwc: Reduce DT reads by allocating host bridge via DWC glue driver

Krishna Chaitanya Chundru
2025-01-24T08:26:42Z

On 1/24/2025 11:48 AM, Manivannan Sadhasivam wrote:
> On Tue, Jan 21, 2025 at 02:32:21PM +0530, Krishna Chaitanya Chundru wrote:
>> Allow DWC glue drivers to allocate the host bridge, avoiding redundant
>> device tree reads primarily in dw_pcie_ecam_supported().
>>
>
> I don't understand what you mean by 'redundant device tree reads'. Please
> explain.
>
In dw_pcie_ecam_supported () we are trying to read bus-range to find
maximum bus range value. devm_pci_alloc_host_bridge() is already reading
bus range it. If we move devm_pci_alloc_host_bridge() to start of the
controller probe we can avoid reading the dt and use values stored in
the host bridge.
This was recommended by bjorn in the v2.

I will update the commit text in the next series.
> - Mani
>
>> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
>> ---
>> drivers/pci/controller/dwc/pcie-designware-host.c | 13 +++++++------
>> 1 file changed, 7 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
>> index 3888f9fe5af1..0acf9db44f2c 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;
>>
>> @@ -497,11 +497,12 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>> return -ENODEV;
>> }
>>
>> - bridge = devm_pci_alloc_host_bridge(dev, 0);
>> - 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;
>> + }
>>
>> pp->cfg0_size = resource_size(res);
>> pp->cfg0_base = res->start;
>>
>> --
>> 2.34.1
>>
>