linux-kernel - Re: [PATCH v2 5/7] usb: dwc3: Add snps,ref-clock-frequency-hz property for ACPI

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Message-ID: <e808f3e2-55ad-e8bb-097c-81e4a82d0bb2@seco.com>
Date:   Mon, 24 Jan 2022 18:07:53 -0500
From:   Sean Anderson <sean.anderson@...o.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Balaji Prakash J <bjagadee@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Robert Hancock <robert.hancock@...ian.com>,
        Baruch Siach <baruch@...s.co.il>
Subject: Re: [PATCH v2 5/7] usb: dwc3: Add snps,ref-clock-frequency-hz
 property for ACPI



On 1/24/22 5:44 PM, Thinh Nguyen wrote:
> Sean Anderson wrote:
>> This property allows setting the reference clock frequency properly for
>> ACPI-based systems. It is not documented under dt-bindings, since it is
>> not intended for use on DT-based systems. DT-based systems should use
>> the clocks property instead.
>> 
>> Frequency is preferred over period since it has greater precision when
>> used in calculations.
>> 
>> Signed-off-by: Sean Anderson <sean.anderson@...o.com>
>> ---
>> 
>> Changes in v2:
>> - New
>> 
>>  drivers/usb/dwc3/core.c | 6 ++++--
>>  drivers/usb/dwc3/core.h | 4 +++-
>>  2 files changed, 7 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> index 883e119377f0..5f3dc5f6cbcb 100644
>> --- a/drivers/usb/dwc3/core.c
>> +++ b/drivers/usb/dwc3/core.c
>> @@ -350,8 +350,8 @@ static void dwc3_ref_clk_period(struct dwc3 *dwc)
>>  	u32 reg;
>>  	unsigned long decr, fladj, rate, period;
>>  
>> -	if (dwc->ref_clk) {
>> -		rate = clk_get_rate(dwc->ref_clk);
>> +	if (dwc->ref_clk || dwc->ref_clk_freq) {
>> +		rate = clk_get_rate(dwc->ref_clk) ?: dwc->ref_clk_freq;
>>  		if (!rate)
>>  			return;
>>  		period = NSEC_PER_SEC / rate;
>> @@ -1492,6 +1492,8 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>>  				 &dwc->fladj);
>>  	device_property_read_u32(dev, "snps,ref-clock-period-ns",
>>  				 &dwc->ref_clk_per);
>> +	device_property_read_u32(dev, "snps,ref-clock-frequency-hz",
>> +				 &dwc->ref_clk_freq);
> 
> Please also document in dwc3 DT file whenever we add a new property.

This is intentionally undocumented, as noted in the commit message. 
Rob Herring has said that dt-bindings should only document properties
intended for device-tree.

--Sean