linux-kernel - Re: [v2] musb: omap2430: do not assume balanced enable()/disable()

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Date:   Fri, 9 Sep 2016 22:40:29 +0200
From:   Andreas Kemnade <andreas@...nade.info>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Tony Lindgren <tony@...mide.com>, Bin Liu <b-liu@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2] musb: omap2430: do not assume balanced enable()/disable()

On Fri, 09 Sep 2016 23:21:50 +0300
Laurent Pinchart <laurent.pinchart@...asonboard.com> wrote:

> Hi Tony,
> 
> On Friday 09 Sep 2016 13:08:03 Tony Lindgren wrote:
> > * Laurent Pinchart <laurent.pinchart@...asonboard.com> [160909
> > 12:27]:
> > > On Wednesday 03 Aug 2016 17:38:51 Andreas Kemnade wrote:
> > >> The code assumes that omap2430_musb_enable() and
> > >> omap2430_musb_disable() are called in a balanced way.
> > >> That fact is broken by the fact that musb_init_controller() calls
> > >> musb_platform_disable() to switch from unknown state to off state
> > >> on initialisation.
> > >> 
> > >> That means that phy_power_off() is called first so that
> > >> phy->power_count gets -1 and the phy is not enabled on
> > >> phy_power_on(). So when usb gadget is started the phy is not
> > >> powered on. Depending on the phy used that caused various
> > >> problems. Besides of causing usb problems, that can also have
> > >> side effects.
> > >> 
> > >> In the case of using the phy_twl4030, that prevents also charging
> > >> the battery via usb (using twl4030_charger) and so makes further
> > >> kernel debugging hard.
> > >> The problem was seen with 4.7 on an openphoenux gta04. It has a
> > >> DM3730 SoC and a TPS65950 companion.  phy->power never became 1
> > >> and so the usb did get powered on.
> > >> 
> > >> The patch prevents phy_power_off() from being called when
> > >> it is already off.
> > >> 
> > >> Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> > > 
> > > This fixes USB gadget operation on the Panda board.
> > > 
> > > Fixes: a83e17d0f73b ("usb: musb: Improve PM runtime and phy
> > > handling for 2430 glue layer")
> > > Tested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > 
> > This patch has a side effect of fixing the issue by breaking PM
> > runtime, not a good fix as discussed.
> 
> How exactly is it worse breaking runtime PM than breaking USB gadget 
> completely ? :-)
> 
Does it still break with my phy-twl4030 fixes? At least on gta04,
they fix real problems and hide the musb problem I tried to fix with
this patch.
https://patchwork.kernel.org/patch/9292097/
https://patchwork.kernel.org/patch/9298447/

> The issue here is that the .disable() platform operation is called by
> musb with the PHY already powered off, leading to the PHY power
> reference count becoming negative. The next call to the .enable()
> operation restores the reference count to 0 without enabling the PHY.
> 
> Feel free to send me a better fix and I will test it.
> 
The patch has to be reworked on top of the patch series:
Implement PM runtime for musb-core based on session bit

Regards,
Andreas Kemnade