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Subject: Re: [PATCH v2 5/7] usb: dwc3: Add snps,ref-clock-frequency-hz
 property for ACPI
From:   Sean Anderson <sean.anderson@seco.com>
To:     Thinh Nguyen <Thinh.Nguyen@synopsys.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>
Cc:     Felipe Balbi <balbi@kernel.org>,
        Balaji Prakash J <bjagadee@codeaurora.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Robert Hancock <robert.hancock@calian.com>,
        Baruch Siach <baruch@tkos.co.il>, Rob Herring <robh@kernel.org>
References: <20220119002438.106079-1-sean.anderson@seco.com>
 <20220119002438.106079-6-sean.anderson@seco.com>
 <5275ea80-400e-d1de-f03e-c2ea81f959dc@synopsys.com>
 <e808f3e2-55ad-e8bb-097c-81e4a82d0bb2@seco.com>
Message-ID: <6ffae12d-3116-c4f2-09c3-32e448bb4717@seco.com>
Date:   Mon, 24 Jan 2022 18:14:51 -0500
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On 1/24/22 6:07 PM, Sean Anderson wrote:
> 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@seco.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.

context: https://lore.kernel.org/all/20181219202734.GA31178@bogus/

This patch was later resubmitted as 24bc6e68efa0 ("serial: sc16is7xx: 
Respect clock-frequency property") without the dt-bindings documentation.

+CC Rob if he wants to comment on this specific situation.

--Sean