lkml.org 
[lkml]   [2013]   [Apr]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRE: [PATCH v2 1/7] ARM: tegra: finalize USB EHCI and PHY bindings
> -----Original Message-----
> From: linux-tegra-owner@vger.kernel.org [mailto:linux-tegra-
> owner@vger.kernel.org] On Behalf Of Stephen Warren
> Sent: Thursday, April 04, 2013 12:38 AM
> To: Venu Byravarasu
> Cc: gregkh@linuxfoundation.org; balbi@ti.com;
> stern@rowland.harvard.edu; linux-tegra@vger.kernel.org; linux-
> usb@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v2 1/7] ARM: tegra: finalize USB EHCI and PHY bindings
>
> On 04/03/2013 02:41 AM, Venu Byravarasu wrote:
> > The existing Tegra USB bindings have a few issues:
> ...
> > This patch fixes the binding definition to resolve these issues.
>
> > diff --git a/Documentation/devicetree/bindings/usb/nvidia,tegra20-usb-
> phy.txt b/Documentation/devicetree/bindings/usb/nvidia,tegra20-usb-
> phy.txt
>
> > Required properties :
> ...
> > + - vbus-supply: regulator for VBUS
>
> Doesn't the driver only need to control VBUS if the port is in OTG mode?
>
> If there is no VBUS control, and the HW provides VBUS, I think that the
> port can only operate in host mode.
>
> If there is no VBUS control, and the HW does not provide VBUS, I think
> that the port can only operate in peripheral mode.
>
> If there is VBUS control, then shouldn't the port always operate in OTG
> mode, or are there other reasons to control VBUS even in host-only mode?
>
> If VBUS control is only useful for OTG mode, then I think the
> vbus-supply property should be documented in a "Required properties for
> dr_mode == otg" section.

Agree, will do it in next patch update.

>
> I assume that VBUS control makes no sense for a peripheral-mode-only
> port, so if VBUS control is useful for host-only mode as well as OTG
> mode, then I think the vbus-supply property should be documented in a
> "Required properties for dr_mode != peripheral" section.
>
> Is the following table correct?
>
> Port operating mode: host peripheral otg
> -------------------- ---- ---------- ---
> VBUS control required: no no yes
> VBUS control useful: yes[1]? no yes
>
> [1] perhaps for power-saving/suspend???

For waking system up from sleep via devices connected to USB, I think Vbus is always
kept ON in host mode.

> --
> To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html


\
 
 \ /
  Last update: 2013-04-04 15:01    [W:0.056 / U:0.004 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site