Re: [PATCH 0/6] usb: dwc3: Calculate REFCLKPER et. al. from reference clock

From: Robert Hancock
Date: Mon Jan 17 2022 - 18:50:26 EST


On Mon, 2022-01-17 at 20:30 +0800, Jun Li wrote:
> Sean Anderson <sean.anderson@xxxxxxxx> 于2022年1月15日周六 10:11写道:
> > 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.
>
> DWC3 databook states a *condition* for program those settings:
>
> This field must be programmed to a non-zero value only if
> GFLADJ_REFCLK_LPM_SEL is set to '1' or GCTL.SOFITPSYNC is set to '1'.
> The value is derived as follows:
> FLADJ_REF_CLK_FLADJ=((125000/ref_clk_period_integer)-(125000/ref_clk_period))
> * ref_clk_period where
> ■ the ref_clk_period_integer is the integer value of the ref_clk
> period got by truncating the decimal (fractional) value that is
> programmed in the GUCTL.REF_CLK_PERIOD field.
> ■ the ref_clk_period is the ref_clk period including the fractional value.
>
> So you may need a condition check, with that, only required users
> are effected even with "ref" clock specified.
>

The Xilinx register documentation for this register in the DWC3 core (
https://www.xilinx.com/html_docs/registers/ug1087/usb3_xhci___gfladj.html ) has
the same description, but it is rather confusingly worded. I suspect what they
really mean is that "this field only needs to be programmed if
GFLADJ_REFCLK_LPM_SEL is set to '1' or GCTL.SOFITPSYNC is set to '1'", not
"this field should only be programmed if GFLADJ_REFCLK_LPM_SEL is set to '1' or
GCTL.SOFITPSYNC is set to '1'". I'm not sure if someone can confirm that
interpretation is correct?

However, looking at that description a bit further, it looks like there are
some other fields in that register which are dependent on the reference clock:
GFLADJ_REFCLK_240MHZ_DECR (bits 30:24) and GFLADJ_REFCLK_240MHZDECR_PLS1 (bit
31). It looks like the Xilinx board I am using has those set properly, i.e. to
12 and 0 respectively (I'm guessing by hardware default, since I don't see
anything in the FSBL psu_init code setting those), but it wouldn't hurt to
ensure those fields are also set correctly.

> Li Jun
>
> > [1]
> > https://urldefense.com/v3/__https://lore.kernel.org/linux-usb/20220114044230.2677283-1-robert.hancock@xxxxxxxxxx/__;!!IOGos0k!387DmPelOIA5Z6ZSfzSF2spWPu3lARlrkdmIRGcPwlWDZGDQzdlEdEKBw1RWG8aRC38$
> >
> >
> >
> > Sean Anderson (6):
> > dt-bindings: usb: dwc3: Deprecate snps,ref-clock-period-ns
> > usb: dwc3: Get clocks individually
> > usb: dwc3: Calculate REFCLKPER based on reference clock
> > usb: dwc3: Handle fractional reference clocks
> > arm64: dts: zynqmp: Move USB clocks to dwc3 node
> > arm64: dts: ipq6018: Use reference clock to set dwc3 period
> >
> > .../devicetree/bindings/usb/snps,dwc3.yaml | 7 +-
> > arch/arm64/boot/dts/qcom/ipq6018.dtsi | 3 +-
> > .../arm64/boot/dts/xilinx/zynqmp-clk-ccf.dtsi | 4 +-
> > arch/arm64/boot/dts/xilinx/zynqmp.dtsi | 4 +-
> > drivers/usb/dwc3/core.c | 98 ++++++++++++++++---
> > drivers/usb/dwc3/core.h | 6 +-
> > 6 files changed, 98 insertions(+), 24 deletions(-)
> >
> > --
> > 2.25.1
> >
--
Robert Hancock
Senior Hardware Designer, Calian Advanced Technologies
www.calian.com