linux-kernel - Re: [PATCH 4/6] usb: phy: tegra: Program new PHY parameters

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Message-ID: <51FBBCB1.9060906@nvidia.com>
Date:	Fri, 2 Aug 2013 17:05:37 +0300
From:	Tuomas Tynkkynen <ttynkkynen@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	<balbi@...com>, <linux-tegra@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	<gregkh@...uxfoundation.org>, <stern@...land.harvard.edu>
Subject: Re: [PATCH 4/6] usb: phy: tegra: Program new PHY parameters

On 08/02/2013 12:16 AM, Stephen Warren wrote:
> On 07/31/2013 11:42 AM, Tuomas Tynkkynen wrote:
>> The Tegra30 TRM recommends configuration of certain PHY parameters for
>> optimal quality. Program the following registers based on device tree
>> parameters:
>>
>> - UTMIP_XCVR_HSSLEW: HS slew rate control.
>> - UTMIP_HSSQUELCH_LEVEL: HS squelch detector level
>> - UTMIP_HSDISCON_LEVEL: HS disconnect detector level.
>>
>> These registers exist in Tegra20, but programming them hasn't been
>> necessary, so these parameters won't be set on Tegra20 to keep the
>> device trees backward compatible.
>>
>> Additionally, the UTMIP_XCVR_SETUP parameter can be set from fuses
>> instead of a software-programmed value, as the optimal value can
>> vary between invidual boards. The boolean property
>> nvidia,xcvr-setup-use-fuses can be used to enable this behaviour.
> 
>> diff --git a/drivers/usb/phy/phy-tegra-usb.c b/drivers/usb/phy/phy-tegra-usb.c

> Those two chunks end up clearing some fields in the register now even on
> earlier chips, whereas before their values were maintained when doing
> the read/modify/write. Yet, the commit description says the new fields
> aren't changed on Tegra20. Do the changes above need to be guarded by if
> (requires_extra_tuning_parameters)?

Oops, you are right. I overlooked that some of those fields have non-zero reset values.
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