linux-kernel - Re: [PATCH v4 3/5] dt-bindings: phy: tegra: Add Tegra194 support

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Date:   Thu, 17 Oct 2019 15:48:52 +0800
From:   JC Kuo <jckuo@...dia.com>
To:     Rob Herring <robh@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jon Hunter <jonathanh@...dia.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        <linux-tegra@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        Nagarjuna Kristam <nkristam@...dia.com>
Subject: Re: [PATCH v4 3/5] dt-bindings: phy: tegra: Add Tegra194 support

Hi Thierry, Hi Rob, Hi Kishon,
Please let me know your thoughts of the below implementation.

1. Add a "bool disable_gen2" to "phy->attrs" structure.
2. In _of_phy_get() of phy-core.c to add the follow to parse a generic property.

	phy->attrs.disable_gen2 = of_property_read_bool(args.np,
							"usb-disable-gen2");
3. In individual phy driver, to add SOC/PHY specific programming accordingly.

Thanks,
JC

On 10/14/19 9:40 PM, Rob Herring wrote:
> On Mon, Oct 14, 2019 at 8:17 AM Thierry Reding <thierry.reding@...il.com> wrote:
>>
>> On Wed, Oct 09, 2019 at 06:39:00PM -0500, Rob Herring wrote:
>>> On Wed, Oct 09, 2019 at 10:43:41AM +0800, JC Kuo wrote:
>>>> Extend the bindings to cover the set of features found in Tegra194.
>>>> Note that, technically, there are four more supplies connected to the
>>>> XUSB pad controller (DVDD_PEX, DVDD_PEX_PLL, HVDD_PEX and HVDD_PEX_PLL)
>>>> , but the power sequencing requirements of Tegra194 require these to be
>>>> under the control of the PMIC.
>>>>
>>>> Tegra194 XUSB PADCTL supports up to USB 3.1 Gen 2 speed, however, it is
>>>> possible for some platforms have long signal trace that could not
>>>> provide sufficient electrical environment for Gen 2 speed. To deal with
>>>> this, a new device node property "nvidia,disable-gen2" was added to
>>>> Tegra194 that be used to specifically disable Gen 2 speed for a
>>>> particular USB 3.0 port so that the port can be limited to Gen 1 speed
>>>> and avoid the instability.
>>>
>>> I suspect this may be a common issue and we should have a common
>>> property. Typically, this kind of property is in the controller though
>>> and supports multiple speed limits. See PCI bindings for inspiration.
>>
>> Given that support for gen 2 speeds is dependent on signal trace length,
>> it doesn't really make sense to restrict the whole controller to a given
>> speed if only the signal trace for a single port exceeds the limit for
>> which gen 2 would work.
>>
>> Also, the USB PHYs are in a different hardware block than the USB
>> controller, so this really is a property of the PHY block, not the USB
>> controller.
> 
> Okay, but still should be common for USB PHYs IMO.
> 
> Rob
>