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

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Message-ID: <6e35eea5-2c7b-5d71-f39d-f9196a3c1b76@quicinc.com>
Date: Fri, 24 Jan 2025 13:56:25 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Manivannan Sadhasivam <mani@...nel.org>,
        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>,
        Manivannan Sadhasivam
	<manivannan.sadhasivam@...aro.org>,
        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_vpernami@...cinc.com>,
        <quic_mrana@...cinc.com>, <mmareddy@...cinc.com>
Subject: Re: [PATCH v3 3/4] PCI: dwc: Reduce DT reads by allocating host
 bridge via DWC glue driver



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@....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
>>
>