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From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: linux-usb@vger.kernel.org,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	Rob Herring <robh@kernel.org>, Roger Quadros <rogerq@ti.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Jassi Brar <jaswinder.singh@linaro.org>,
	Kunihiko Hayashi <hayashi.kunihiko@socionext.com>,
	devicetree@vger.kernel.org, Felipe Balbi <balbi@kernel.org>,
	linux-kernel@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v2 2/2] usb: dwc3: support clocks and resets for DWC3 core
Date: Mon, 23 Apr 2018 19:44:27 +0200	[thread overview]
Message-ID: <CAFBinCDwbyovMZ-qAKaMiBfz_YKMwxC1c4MjfNyLAvnXEfXtMw@mail.gmail.com> (raw)
In-Reply-To: <1524135818-14825-3-git-send-email-yamada.masahiro@socionext.com>

Hello,

On Thu, Apr 19, 2018 at 1:03 PM, Masahiro Yamada
<yamada.masahiro@socionext.com> 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"

> Supporting those clocks and resets is the requirement for new platforms.
just to confirm:
with this series your goal is to replace the wrapper node which is
needed due to dwc3-of-simple.c ?
would other drivers which currently create a wrapper node (like
dwc3-keystone.c) keep their wrapper node or do you have any plans for
removing it for the other "wrapper" drivers too?

> Enforcing the new binding breaks existing platforms since they specify
> clocks and resets in their glue layer node, but nothing in the core
> node.  I listed such exceptional cases in the DT binding.  The driver
> code is loosened up to accept no clock/reset.  This change is based
> on the discussion [1].
(snip)

Regards
Martin

  reply	other threads:[~2018-04-23 17:44 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-19 11:03 [PATCH v2 0/2] " Masahiro Yamada
2018-04-19 11:03 ` [PATCH v2 1/2] usb: dwc3: use local copy of resource to fix-up register offset Masahiro Yamada
2018-05-01 14:07   ` Masahiro Yamada
2018-04-19 11:03 ` [PATCH v2 2/2] usb: dwc3: support clocks and resets for DWC3 core Masahiro Yamada
2018-04-23 17:44   ` Martin Blumenstingl [this message]
2018-04-24  1:17     ` Masahiro Yamada
2018-04-28  2:41     ` Masahiro Yamada
2018-04-28 14:20       ` Martin Blumenstingl
2018-05-10  9:24         ` Masahiro Yamada
2018-04-25 15:21   ` Rob Herring
2018-04-27 16:20     ` Masahiro Yamada
2018-04-27 18:40       ` Rob Herring
2018-04-24  0:11 ` [PATCH v2 0/2] " Manu Gautam
2018-04-24  1:36   ` Masahiro Yamada

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