linux-kernel - Re: [RFC 0/5] usb: chipidea: Add support for Tegra20 through Tegra124

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Message-ID: <20160527031624.GA3034@shlinux2>
Date:	Fri, 27 May 2016 11:16:24 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Peter Chen <Peter.Chen@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Jon Hunter <jonathanh@...dia.com>, linux-usb@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 0/5] usb: chipidea: Add support for Tegra20 through Tegra124

On Thu, May 26, 2016 at 05:40:00PM +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@...dia.com>
> 
> All Tegra SoC generations from Tegra20 through Tegra124 have a ChipIdea
> USB device controller. This set of patches adds very rudimentary support
> for it to the existing ChipIdea driver and enables them on the set of
> boards that I could easily test on.
> 
> I'm sending this out as RFC because I'm not sure yet how to merge this.
> While the driver seems to work fine (tested by exporting a USB driver or
> eMMC via the mass storage function) I don't yet understand how to make
> the driver switch between host and device modes dynamically. It might be
> useful to get this merged before, but I'd like to have some feedback on
> this, because doing so would mean that we need to use device mode on the
> devices where it's enabled and can't use the USBD port in host mode.
> 

Chipidea driver supports many ways to switch between host and device
mode. It can support switching with/without disconnecting cable.

Most of cases need to disconnect cable (Micro-AB) to switch between
host and device mode, I just take this as an example:

Using ID pin which is at Micro-B receptacle on the board to determine host (ID = 0)
or device (ID = 1 )mode.

- ID pin connects to CPU, and ID interrupt and value can be get through
register OTGSC.
- ID pin does not connect to CPU, and there is a dedicated GPIO for ID.

-- 

Best Regards,
Peter Chen