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Subject: Re: [PATCH V3 4/6] usb: ohci-platform: Add support for Broadcom STB
 SoC's
To:     Al Cooper <al.cooper@broadcom.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Alan Stern <stern@rowland.harvard.edu>
Cc:     Al Cooper <alcooperx@gmail.com>, linux-kernel@vger.kernel.org,
        Alban Bedel <albeu@free.fr>, Alex Elder <elder@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Avi Fishman <avifishman70@gmail.com>,
        bcm-kernel-feedback-list@broadcom.com,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Chunfeng Yun <chunfeng.yun@mediatek.com>,
        "David S. Miller" <davem@davemloft.net>,
        devicetree@vger.kernel.org, Dmitry Osipenko <digetx@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        Hans de Goede <hdegoede@redhat.com>,
        James Hogan <jhogan@kernel.org>,
        Jianguo Sun <sunjianguo1@huawei.com>,
        Johan Hovold <johan@kernel.org>,
        Kees Cook <keescook@chromium.org>, linux-usb@vger.kernel.org,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
        Mathias Nyman <mathias.nyman@intel.com>,
        Mathias Nyman <mathias.nyman@linux.intel.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Rishabh Bhatnagar <rishabhb@codeaurora.org>,
        Rob Herring <robh+dt@kernel.org>, Roger Quadros <rogerq@ti.com>
References: <Pine.LNX.4.44L0.1811071124260.1542-100000@iolanthe.rowland.org>
 <16a80878-58f7-1584-058e-0e0e49da61cb@gmail.com>
 <45134862-4b72-be72-533c-942c2bf70400@broadcom.com>
From:   Florian Fainelli <f.fainelli@gmail.com>
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Message-ID: <c551a2e2-c494-04d3-53cf-f027b02906ed@gmail.com>
Date:   Wed, 7 Nov 2018 10:11:59 -0800
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On 11/7/2018 9:40 AM, Al Cooper wrote:
> 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@gmail.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.

So in that regard the Device Tree property would actually scale a bit
better in that you would no longer need to modify the various
*hci-plat*.c files, if that is the way to go, then sure.
-- 
Florian