linux-kernel - Re: [PATCH RFC 7/7] pci: pwrctl: Add power control driver for qps615

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Message-ID: <75dd875c-bc08-3f18-2f94-5d4c1851aff3@quicinc.com>
Date: Sat, 3 Aug 2024 08:48:22 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@...aro.org>,
        Bartosz Golaszewski
	<brgl@...ev.pl>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring
	<robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Krzysztof Kozlowski
	<krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>
CC: <quic_vbadigan@...cinc.com>, <quic_skananth@...cinc.com>,
        <quic_nitegupt@...cinc.com>, <linux-arm-msm@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 7/7] pci: pwrctl: Add power control driver for qps615



On 6/26/2024 9:07 PM, Konrad Dybcio wrote:
> On 26.06.2024 2:37 PM, Krishna chaitanya chundru wrote:
>> QPS615 switch needs to configured after powering on and before
>> PCIe link was up.
>>
>> As the PCIe controller driver already enables the PCIe link training
>> at the host side, stop the link training.
>> Otherwise the moment we turn on the switch it will participate in
>> the link training and link may come before switch is configured through
>> i2c.
>>
>> The switch can be configured different ways like changing de-emphasis
>> settings of the switch, disabling unused ports etc and these settings
>> can vary from board to board, for that reason the sequence is taken
>> from the firmware file which contains the address of the slave, to address
>> and data to be written to the switch. The driver reads the firmware file
>> and parses them to apply those configurations to the switch.
>>
>> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
>> ---
> 
> [...]
> 
>> +static int qcom_qps615_pwrctl_init(struct qcom_qps615_pwrctl_ctx *ctx)
>> +{
>> +	struct device *dev = ctx->pwrctl.dev;
>> +	struct qcom_qps615_pwrctl_i2c_setting *set;
>> +	const struct firmware *fw;
>> +	const u8 *pos, *eof;
>> +	int ret;
>> +	u32 val;
>> +
>> +	ret = request_firmware(&fw, "qcom/qps615.bin", dev);
> 
> Is this driver only going to serve one model of the device, that will use
> this specific firmware file, ever?
> 
> In other words, is QPS615 super special and no other chip like it will be
> ever made?
> 
> [...]
> 
>> +
>> +	bridge->ops->stop_link(bus);
> 
> This is turbo intrusive. What if there are more devices on this bus?
> 
The expectation of this API from the controller driver is to stop link
training only when the link is not up.

- krishna chaitanya.
> Konrad