linux-kernel - Re: [PATCH V3 4/6] usb: ohci-platform: Add support for Broadcom STB SoC's

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Message-ID: <Pine.LNX.4.44L0.1811071124260.1542-100000@iolanthe.rowland.org>
Date:   Wed, 7 Nov 2018 11:27:26 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Al Cooper <al.cooper@...adcom.com>
cc:     Florian Fainelli <f.fainelli@...il.com>,
        Al Cooper <alcooperx@...il.com>,
        <linux-kernel@...r.kernel.org>, Alban Bedel <albeu@...e.fr>,
        Alex Elder <elder@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Avi Fishman <avifishman70@...il.com>,
        <bcm-kernel-feedback-list@...adcom.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        "David S. Miller" <davem@...emloft.net>,
        <devicetree@...r.kernel.org>, Dmitry Osipenko <digetx@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Hans de Goede <hdegoede@...hat.com>,
        James Hogan <jhogan@...nel.org>,
        Jianguo Sun <sunjianguo1@...wei.com>,
        Johan Hovold <johan@...nel.org>,
        Kees Cook <keescook@...omium.org>, <linux-usb@...r.kernel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Rishabh Bhatnagar <rishabhb@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>, Roger Quadros <rogerq@...com>
Subject: Re: [PATCH V3 4/6] usb: ohci-platform: Add support for Broadcom STB
 SoC's

On Wed, 7 Nov 2018, Al Cooper wrote:

> On 11/7/18 10:23 AM, Alan Stern wrote:
> > On Tue, 6 Nov 2018, Florian Fainelli wrote:
> > 
> >> On 11/6/18 1:40 PM, Al Cooper wrote:
> >>> On 11/6/18 11:08 AM, Alan Stern wrote:
> >>>> On Mon, 5 Nov 2018, Al Cooper wrote:
> >>>>
> >>>>> Add support for Broadcom STB SoC's to the ohci platform driver.
> >>>>>
> >>>>> Signed-off-by: Al Cooper <alcooperx@...il.com>
> >>>>> ---
> >>>>
> >>>>> @@ -177,6 +189,8 @@ static int ohci_platform_probe(struct
> >>>>> platform_device *dev)
> >>>>>            ohci->flags |= OHCI_QUIRK_FRAME_NO;
> >>>>>        if (pdata->num_ports)
> >>>>>            ohci->num_ports = pdata->num_ports;
> >>>>> +    if (pdata->suspend_without_phy_exit)
> >>>>> +        hcd->suspend_without_phy_exit = 1;
> >>>>
> >>>> Sorry if I missed this in the earlier discussions...  Is there any
> >>>> possibility of adding a DT binding that could express this requirement,
> >>>> instead of putting it in the platform data?
> >>>>
> >>>> Alan Stern
> >>>>
> >>>
> >>> Alan,
> >>>
> >>> That was my original approach but internal review suggested that I use
> >>> pdata instead. Below is my original patch for:
> >>
> >> And the reason for that suggestion was really because it was percevied
> >> as encoding a driver behavior as a Device Tree property as opposed to
> >> describing something that was inherently and strictly a hardware
> >> behavior (therefore suitable for Device Tree).
> > 
> > Right.  The best way to approach this problem is to identify and
> > characterize the hardware behavior which makes this override necessary.
> > Then _that_ can be added to DT, since it will be a property of the
> > hardware rather than of the driver.
> > 
> >>> Add the ability to skip calling the PHY's exit routine on suspend
> >>> and the PHY's init routine on resume. This is to handle a USB PHY
> >>> that should have it's power_off function called on suspend but cannot
> >>> have it's exit function called because on exit it will disable the
> >>> PHY to the point where register accesses to the Host Controllers
> >>> using the PHY will be disabled and the host drivers will crash.
> > 
> > What's special about this PHY?  Why does the exit function mess the PHY
> > up?  Or to put it another way, why doesn't the exit function mess up
> > other PHYs in the same way?
> > 
> > For that matter, can we change the code so that suspend doesn't call
> > the exit function for _any_ PHY?  Will just calling the power_off
> > function be good enough?  If not, then why not?
> > 
> > Alan Stern
> > 
> 
> In our USB hardware the USB PHY supplies a clock for the EHCI/OHCI and 
> XHCI host controllers and if the PHY is totally shut down the EHCI, OHCI 
> and XHCI registers will cause an exception if accessed and cause the 
> EHCI, OHCI and XHCI drivers to crash. There is always talk of fixing 
> this in the hardware by adding an aux clock that will takeover when the 
> PHY clock is shut down, but this hasn't happened yet. It seems like 
> "exit on suspend" still makes sense on systems that don't have this 
> problem (additional power savings?) so removing the exit on suspend for 
> all systems is not a good idea.

Then in theory you should be able to add a Device Tree property which
says that the PHY provides a clock for the USB host controller.  That
is strictly a property of the hardware; it has nothing to do with the
driver.  Therefore it is appropriate for DT.

Wouldn't this solve your issue?

Alan Stern