Re: [PATCH v2 2/2] usb: dwc3: support clocks and resets for DWC3 core

From: Masahiro Yamada
Date: Fri Apr 27 2018 - 22:41:59 EST

Hi Martin,

2018-04-24 2:44 GMT+09:00 Martin Blumenstingl
> Hello,
> On Thu, Apr 19, 2018 at 1:03 PM, Masahiro Yamada
> <yamada.masahiro@xxxxxxxxxxxxx> wrote:
>> Historically, the clocks and resets are handled on the glue layer
>> side instead of the DWC3 core. For simple cases, dwc3-of-simple.c
>> takes care of arbitrary number of clocks and resets. The DT node
>> structure typically looks like as follows:
>> dwc3-glue {
>> compatible = "foo,dwc3";
>> clocks = ...;
>> resets = ...;
>> ...
>> dwc3 {
>> compatible = "snps,dwc3";
>> ...
>> };
>> }
>> By supporting the clocks and the reset in the dwc3/core.c, it will
>> be turned into a single node:
>> dwc3 {
>> compatible = "foo,dwc3", "snps,dwc3";
>> clocks = ...;
>> resets = ...;
>> ...
>> }
>> This commit adds the binding of clocks and resets specific to this IP.
>> The number of clocks should generally be the same across SoCs, it is
>> just some SoCs either tie clocks together or do not provide software
>> control of some of the clocks.
>> I took the clock names from the Synopsys datasheet: "ref" (ref_clk),
>> "bus_early" (bus_clk_early), and "suspend" (suspend_clk).
> looking at the code: this could mean that dwc3-exynos.c can be removed
> mid-term (assuming the PHY and regulator handling can be
> moved/removed/changed)
> does the datasheet state anything about the clock speeds? from
> Documentation/devicetree/bindings/usb/dwc3-xilinx.txt:
> "bus_clk" Master/Core clock, have to be >= 125 MHz for SS operation
> and >= 60MHz for HS operation
>> I found only one reset line in the datasheet, hence the reset-names
>> property is omitted.
> does the datasheet state whether this is a level or a pulsed reset line?
> on Amlogic Meson GXL, GXM and AXG SoCs we use a pulsed (and shared)
> reset line (see ff0a632f08759e "usb: dwc3: of-simple: add support for
> shared and pulsed reset lines") because the reset line is shared
> between various components (USB2 PHY, USB3 PHY, dwc3 controller, ...)
> your current approach (having a vendor-specific "foo,dwc3" binding
> along with the generic "snps,dwc3") would allow having
> per-"of_device_id" settings which could indicate whether the reset
> lines are level or pulsed reset if these are "implementation specific"

Let me ask a question about your reset controller.

All reset ID supports .reset, .assert, .deassert
Is this correct?

I believe you and I use the same DWC3 core IP.

I suspect the difference is in the reset controller side.

In my case, the reset line is asserted by default.
(that is, all FFs in the RTL are put into the initial state
on power-on)
That's why only reset_deassert() will work for me, I think.

What about your case? Is the reset line in deassert state on power-on?
Then, the reset must be explicitly pulsed to put FFs into
the initial state. Is this correct?

Best Regards
Masahiro Yamada