linux-kernel - Re: [PATCH v2 06/11] phy: da8xx-usb: new driver for DA8XX SoC USB PHY

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Date:	Fri, 1 Apr 2016 14:56:35 -0500
From:	Bin Liu <b-liu@...com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
CC:	David Lechner <david@...hnology.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Petr Kulhavy <petr@...ix.com>,
	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>,
	Russell King <linux@....linux.org.uk>,
	Sekhar Nori <nsekhar@...com>,
	Kevin Hilman <khilman@...nel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andreas Färber <afaerber@...e.de>,
	Tony Lindgren <tony@...mide.com>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v2 06/11] phy: da8xx-usb: new driver for DA8XX SoC USB PHY

Hi,

On Fri, Apr 01, 2016 at 10:45:47PM +0300, Sergei Shtylyov wrote:
> On 04/01/2016 07:02 PM, David Lechner wrote:
> 
> >>>>+EXPORT_SYMBOL_GPL(da8xx_usb20_phy_set_mode);
> >>>
> >>>Don't prefer export symbols from PHY driver. That'll create unnecessary
> >>>dependencies between the controller and the PHY.
> >>
> >>Agreed.
> >>
> >>>I think it'll be better to create a new attribute and use it?
> >>
> >>Another simpler option is to not support _set_mode() for DA8xx, and the
> >>phy driver set the otgmode bit in probe() based on dr_mode of the
> >>controller.
> >>
> >>Regards,
> >>-Bin.
> >
> >This certainly works for my particular use case, however, Sergei Shtylyov, who
> >wrote the da8xx musb glue layer originally, seemed to recall in his review of
> >the patch series that this really is necessary for OTG mode to work properly.
> 
>    No, it's still not necessary, however this method is now called
> from musb_init_controller() (it wasn't in my time). ISTR however
> that you needed to enforce the mode override in CFGCHIP2 for the
> host mode to function properly.

Yes, but I think we don't have to rely on musb_init_controller(), what
we can do is the phy probe() calls of_usb_get_dr_mode_by_phy() to get
the dr_mode of the controller then sets CFGCHIP2 bits accordingly, so
that we can drop _set_mode() in the phy driver.

Regards,
-Bin.