linux-kernel - Re: [PATCH 6/6] arm64: tegra: Add support for PCIe endpoint mode in P2972-0000 platform

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Message-ID: <e1e44c1c-c1ab-27dd-b3ac-a9ed878411a2@nvidia.com>
Date:   Mon, 25 Nov 2019 12:30:53 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     <lorenzo.pieralisi@....com>, <bhelgaas@...gle.com>,
        <robh+dt@...nel.org>, <jonathanh@...dia.com>,
        <andrew.murray@....com>, <kishon@...com>,
        <gustavo.pimentel@...opsys.com>, <linux-pci@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <kthota@...dia.com>,
        <mmaddireddy@...dia.com>, <sagar.tv@...il.com>
Subject: Re: [PATCH 6/6] arm64: tegra: Add support for PCIe endpoint mode in
 P2972-0000 platform

On 11/22/2019 6:55 PM, Thierry Reding wrote:
> On Fri, Nov 22, 2019 at 04:15:05PM +0530, Vidya Sagar wrote:
>> Add endpoint mode support for PCIe C5 controller in P2972-0000 platform
>> with information about supplies, PHY, PERST GPIO and GPIO that controls
>> PCIe reference clock coming from the host system.
>>
>> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
>> ---
>>   .../boot/dts/nvidia/tegra194-p2972-0000.dts   | 29 +++++++++++++++++++
>>   1 file changed, 29 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/nvidia/tegra194-p2972-0000.dts b/arch/arm64/boot/dts/nvidia/tegra194-p2972-0000.dts
>> index 7eb64b816e08..58c3a9677bc8 100644
>> --- a/arch/arm64/boot/dts/nvidia/tegra194-p2972-0000.dts
>> +++ b/arch/arm64/boot/dts/nvidia/tegra194-p2972-0000.dts
>> @@ -43,6 +43,19 @@
>>   
>>   		gpio@...0000 {
>>   			status = "okay";
>> +			/*
>> +			 * Change the below node's status to 'okay' when
>> +			 * PCIe C5 controller is enabled to operate in endpoint
>> +			 * to allow REFCLK from the host system to flow into
>> +			 * the controller.
>> +			 */
>> +			pex-refclk-sel-high {
>> +				gpio-hog;
>> +				output-high;
>> +				gpios = <TEGRA194_AON_GPIO(AA, 5) 0>;
>> +				label = "pex_refclk_sel_high";
>> +				status = "disabled";
>> +			};
> 
> Why don't we put this into the PCIe controller's node as a reference to
> that GPIO? Seems like the controller would know exactly when this pin
> needs to go high or low, so why does it have to be a hog?
> 
> Thierry
Are you saying something like 'nvidia,enable-refclk-in'?
I was thinking, since this is like a board level configuration specific to Jetson-Xavier,
it would suffice to just hog it according to the mode of operation of PCIe controller.
But, I see one advantage of referencing it in the PCIe node (so that the driver can configure
it as and when needed) is that one has to be careful just to enable either PCIe RP or EP
node and not worry about other thing (like this).
Let me know if I got this right.

- Vidya Sagar

> 
>>   		};
>>   
>>   		pwm@...0000 {
>> @@ -144,6 +157,22 @@
>>   			    "p2u-5", "p2u-6", "p2u-7";
>>   	};
>>   
>> +	pcie_ep@...a0000 {
>> +		status = "disabled";
>> +
>> +		vddio-pex-ctl-supply = <&vdd_1v8ao>;
>> +
>> +		nvidia,pex-rst-gpio = <&gpio TEGRA194_MAIN_GPIO(GG, 1)
>> +					GPIO_ACTIVE_LOW>;
>> +
>> +		phys = <&p2u_nvhs_0>, <&p2u_nvhs_1>, <&p2u_nvhs_2>,
>> +		       <&p2u_nvhs_3>, <&p2u_nvhs_4>, <&p2u_nvhs_5>,
>> +		       <&p2u_nvhs_6>, <&p2u_nvhs_7>;
>> +
>> +		phy-names = "p2u-0", "p2u-1", "p2u-2", "p2u-3", "p2u-4",
>> +			    "p2u-5", "p2u-6", "p2u-7";
>> +	};
>> +
>>   	fan: fan {
>>   		compatible = "pwm-fan";
>>   		pwms = <&pwm4 0 45334>;
>> -- 
>> 2.17.1
>>