dwc3: add support for hardware with multiple ports on USB2 hub enabled

Martin Blumenstingl martin.blumenstingl at googlemail.com
Mon Jan 9 04:14:00 PST 2017

On Mon, Jan 9, 2017 at 12:55 PM, Felipe Balbi
<felipe.balbi at linux.intel.com> wrote:
> Hi,
> Martin Blumenstingl <martin.blumenstingl at googlemail.com> writes:
>> On Mon, Jan 9, 2017 at 12:18 PM, Felipe Balbi
>> <felipe.balbi at linux.intel.com> wrote:
>>> Hi,
>>> Martin Blumenstingl <martin.blumenstingl at googlemail.com> writes:
>>>>> Martin Blumenstingl <martin.blumenstingl at googlemail.com> writes:
>>>>>> while adding USB support on the Amlogic Meson GXL / GXM SoCs I have
>>>>>> come across something I did not know yet:
>>>>>> dwc3 has an internal USB2 hub (from what I can read in the code there
>>>>>> seem to be multiple USB3 ports supported as well).
>>>>> no, that's not true. It has a roothub when working as host. But that's
>>>>> it. When working as peripheral, it's always single-port AFAIR.
>>>> OK, I should have been more clear here: I am only talking about
>>>> host-mode since DWC3_GHWPARAMS0 on the GXL/GXM SoCs has a value of
>>>> 0x20208009 which translates to "DWC3_GHWPARAMS0_MODE_HOST".
>>>> are you sure about the fact that it does not have an internal hub?
>>>> What I see in both, the vendor kernel's and my own patched mainline
>>>> kernel log is:
>>>> [   19.130331 at 3] xhci-hcd xhci-hcd.0.auto: xHCI Host Controller
>>>> [   19.130385 at 3] xhci-hcd xhci-hcd.0.auto: new USB bus registered,
>>>> assigned bus number 1
>>>> [   19.139666 at 3] xhci-hcd xhci-hcd.0.auto: irq 62, io mem 0xc9000000
>>>> [   19.145295 at 3] hub 1-0:1.0: USB hub found
>>> this is the roothub :-)
>> agreed :)
>>>> [   19.148098 at 3] hub 1-0:1.0: 3 ports detected
>> this is the one I wanted to point out: in this case there are 3 ports
>> on the (USB2) roothub.
>> the SoC has one USB2 for each of these ports, and all 3 PHYs have to
>> be initialized to get USB working (this seems to be my main issue).
>>>> [   19.152396 at 3] xhci-hcd xhci-hcd.0.auto: xHCI Host Controller
>>>> [   19.157813 at 3] xhci-hcd xhci-hcd.0.auto: new USB bus registered,
>>>> assigned bus number 2
>>>> [   19.166598 at 3] hub 2-0:1.0: USB hub found
>>>> [   19.169452 at 3] hub 2-0:1.0: config failed, hub doesn't have any
>>>> ports! (err -19)
>>>> This is from a GXM SoC which also comes with 3x USB2 PHYs (these are
>>>> not Synopsys DesignWare PHYs but custom ones from Amlogic).
>>>> I see similar messages but with "2 ports detect" on a GXL SoC which
>>>> comes with 2x USB2 PHYs.
>>> The fact that is claims that it has "no ports" hints at quirk caused,
>>> likely, by poor RTL edits. coreConsultant should make sure that
>>> MAX_PORTS (in xHCI HCC_PARAMS* register set) was set to correct value,
>>> but somehow that field is set to 0 in one of your Amlogic SoC.
>> yes, it's a USB2-only configuration (so there are no USB3 ports on the
>> internal roothub)
> aha, makes sense.
>>>>>> When searching the web I did not come across any SoC that uses a
>>>>>> configuration with more than one port enabled.
>>>>>> On my Amlogic Meson GXM device (consumer device, no development board)
>>>>>> I see the following USB2 PHY register configuration (full register
>>>>>> dump from the kernel that was shipped with the device is attached):
>>>>>> GUSB2PHYCFG(0) = 0x40102500
>>>>>> GUSB2PHYCFG(1) = 0x40102540
>>>>>> GUSB2PHYCFG(2) = 0x40102540
>>>>> multiple PHYs are only used by the host block (xHCI). Don't touch these
>>>>> and just let xHCI core handle the ports.
>>>> could you be more specific with "xHCI core" - do you mean the core in
>>>> the dwc3 IP or drivers/usb/host/xhci-*?
>>>> However, we still have a "problem" here: the USB PHYs for each
>>>> "enabled" port have to be turned on (if I leave only one USB PHY
>>>> disabled then none of the ports is working). unfortunately the current
>>>> code (both, in dwc3 and drivers/usb/host/*) assumes that there's
>>>> either 0 or 1 PHY for each HCD.
> true. But even so, that PHY handle is only needed for devices which
> weren't properly configured at coreConsultant time.
I don't understand that - there are two separate modules involved
here: 1. the dwc3 IP block 2. Amlogic's own USB2 PHYs (they did not
choose Synopsys DesignWare PHYs)
(some background info: the USB2 PHYs are in "reset mode" by default)
So even if the dwc3 IP block is configured correctly at coreConsultant
time we still need to configure the PHYs. From "USB controller driver"
(could be dwc3, or some generic hcd.c code, etc.) this means that
phy_init() and phy_power_on() needs to be called for each of the three
"Amlogic USB2 PHYs". the current code however only calls these for the
first PHY (leaving the others in reset mode = disabled).

>>>>>> Then vendor kernel sources (a 3.14 kernel) are adding the resets for
>>>>>> GUSB2PHYCFG([1-3]) in dwc3_core_soft_reset().
>>>>> That shouldn't be necessary, actually. If it is, it means the HW was
>>>>> poorly integrated. In that case, we _can_ add the other resets, but I
>>>>> need confirmation that they are needed by means of a public errata
>>>>> document.
>>>>>> A mainline 4.9+(Meson GXL USB PHY patches + dwc3/xhci-plat DMA patches
>>>>>> from linux-usb) kernel works fine even with just applying the reset to
>>>>>> GUSB2PHYCFG(0).
>>>>> there you go
>>>> does that mean that the reset of GUSB2PHYCFG(0) (which is part of the
>>>> current dwc3 code in dwc3_phy_setup) is done only because of the
>>>> quirks/erratas? in other words: do you mean that one would not have to
>>>> reset GUSB2PHYCFG(0) if there were no erratas?
>>> no, it's done for peripheral configuration of dwc3. Look at the code
>>> more carefully:
>> sorry for the confusion - the word "reset" should be "configuration".
>> The function I am looking at is dwc3_phy_setup(): apart from toggling
>> some "errata bits" it also configures the PHY modes. I am wondering if
>> I need to do this setup (DWC3_GUSB2PHYCFG_ULPI_UTMI and
>> DWC3_GUSB2PHYCFG_PHYIF_MASK related bits) not only for the *first*
>> port ("DWC3_GUSB2PHYCFG(0)") but also for the "other" ports (index 1
>> and 2 in above case, where the roothub has 3 ports)
> Ideally, that should've been set at coreConsultant (RTL instantiation)
> time. If it wasn't, then we need to add a quirk for these SoCs
> accordingly. We _do_ need documentation that this quirk is, indeed,
> needed.
That is an explanation I'm fine with: we trust the (default) values
which are in hardware until we have documentation that we need a
quirk. I do not have access to Amlogic's documentation so I can't
provide that - but we can probably leave it as it is as it "worked for

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