linux-kernel - Re: [PATCH v1 5/9] of: Add NVIDIA Tegra XHCI controller binding

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Message-ID: <53AB57ED.7080600@wwwdotorg.org>
Date:	Wed, 25 Jun 2014 17:14:53 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Andrew Bresticker <abrestic@...omium.org>
CC:	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-usb@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Grant Likely <grant.likely@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Kishon Vijay Abraham I <kishon@...com>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v1 5/9] of: Add NVIDIA Tegra XHCI controller binding

On 06/25/2014 05:02 PM, Andrew Bresticker wrote:
> On Wed, Jun 25, 2014 at 2:54 PM, Stephen Warren <swarren@...dotorg.org> wrote:
>> On 06/18/2014 12:16 AM, Andrew Bresticker wrote:
>>> Add device-tree binding documentation for the XHCI controller present
>>> on Tegra124 and later SoCs.
>>
>>> diff --git a/Documentation/devicetree/bindings/usb/nvidia,tegra124-xhci.txt b/Documentation/devicetree/bindings/usb/nvidia,tegra124-xhci.txt
>>
>>> + - clock-names: Must include the following entries:
>>> +    - xusb_host
>>> +    - xusb_falcon_src
>>> +    - xusb_ss
>>> +    - xusb_ss_src
>>> +    - xusb_hs_src
>>> +    - xusb_fs_src
>>
>> Looking at include/dt-bindings/clock/tegra124-car.h I see a few entries
>> potentially missing here:
>>
>> #define TEGRA124_CLK_XUSB_HOST_SRC 252
>> #define TEGRA124_CLK_XUSB_DEV_SRC 256
>> #define TEGRA124_CLK_XUSB_DEV 257
>> #define TEGRA124_CLK_XUSB_SS_DIV2 312
> 
> The driver doesn't use them, so I didn't put them in the binding.

I think we should add them in case we need them later. Best to fully
describe the HW rather than the parts of the HW that SW currently uses.

>>> +    - pll_u_480m
>>
>> Not just pll_u?
> 
> We specifically want pll_u_480M as that's what we use as the parent of
> xusb_ss_src when scaling it to 120Mhz.

OK. I recall text in the TRM implying that SW should just leave PLL_U
alone and not fiddle with the separate output clocks. Still, if we have
a clock ID for each output, and it's the correct parent for the clock,
then it does make sense to use that ID.
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