Date:   Wed, 7 Nov 2018 12:40:57 -0500
From:   Al Cooper <al.cooper@...adcom.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Alan Stern <stern@...land.harvard.edu>
Cc:     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 11/7/18 12:29 PM, Florian Fainelli wrote:
> On 11/7/18 8:27 AM, Alan Stern wrote:
>> 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.
> 
> The very compatible string that is being allocated/defined for this
> controller carries that information already, that is, if you probe a
> "brcm,bcm7445-ohci" compatible then that means the controller has a
> dependency on the PHY to supply its clock.
> 
> Adding a property vs. keying on the compatible string makes sense if you
> know there is at least a second consumer of that property (unless we
> make it a broadcom specific property, in which case, it really is
> redundant with the compatible string).
> 
> Anyway, my grudge with that property was the name chosen initially,
> which included an action to be performed by an implementation as opposed
> to something purely descriptive. E.g: 'phy-supplies-clock' might be okay.
> 
>>
>> Wouldn't this solve your issue?
> 
> It would not change much except that there is no need to much with
> ohci-platform.c anymore, but ultimately that property needs to be read
> by ohci-hcd.c and acted on, which would likely lead to the same amount
> of changes as those present in patch #2 currently.
> 
We also need this functionality in the EHCI and XHCI drivers and it's 
not the ohci-hcd.c module that needs to know, it's the core/phy.c module 
called from core/hcd.c.

Al

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