Message-ID: <16a80878-58f7-1584-058e-0e0e49da61cb@gmail.com>
Date:   Wed, 7 Nov 2018 09:29:42 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        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 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.
-- 
Florian

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