linux-kernel - Re: [PATCH v2 0/7] usb: dwc3: Calculate REFCLKPER et. al. from reference clock

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Date:   Wed, 19 Jan 2022 13:23:44 -0500
From:   Sean Anderson <sean.anderson@...o.com>
To:     Baruch Siach <baruch@...s.co.il>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, Felipe Balbi <balbi@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Balaji Prakash J <bjagadee@...eaurora.org>,
        linux-kernel@...r.kernel.org,
        Robert Hancock <robert.hancock@...ian.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michal Simek <michal.simek@...inx.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 0/7] usb: dwc3: Calculate REFCLKPER et. al. from
 reference clock

Hi Baruch,

On 1/19/22 1:14 PM, Baruch Siach wrote:
> Hi Sean,
>
> On Tue, Jan 18 2022, Sean Anderson wrote:
>> This is a rework of patches 3-5 of [1]. It attempts to correctly program
>> REFCLKPER and REFCLK_FLADJ based on the reference clock frequency. Since
>> we no longer need a special property duplicating this configuration,
>> snps,ref-clock-period-ns is deprecated.
>>
>> Please test this! Patches 3/4 in this series have the effect of
>> programming REFCLKPER and REFCLK_FLADJ on boards which already configure
>> the "ref" clock. I have build tested, but not much else.
>
> Tested here on IPQ6010 based system. USB still works. But the with "ref"
> clock at 24MHz, period is calculated as 0x29. Previous
> snps,ref-clock-period-ns value used to be 0x32.
>
> Is that expected?

Yes. From the documentation for GFLADJ_REFCLK_240MHZ_DECR:

> Examples:
> If the ref_clk is 24 MHz then
> - GUCTL.REF_CLK_PERIOD = 41
> - GFLADJ.GFLADJ_REFCLK_240MHZ_DECR = 240/24 = 10

And 41 == 0x29.

--Sean