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

Martin Blumenstingl martin.blumenstingl at googlemail.com
Sun Nov 27 05:05:09 PST 2016

On Sun, Nov 27, 2016 at 2:02 PM, Martin Blumenstingl
<martin.blumenstingl at googlemail.com> wrote:
> Hello,
> 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).
> 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
> Then vendor kernel sources (a 3.14 kernel) are adding the resets for
> GUSB2PHYCFG([1-3]) in dwc3_core_soft_reset().
> 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
> That brings up two questions:
> 1. I guess it makes sense to adjust the upstream dwc3 to add the
> resets for all available USB2 PHYs - is there a specific reason why
> the current dwc3 driver does not do that (or is it simply because why
> we find on Meson GXL/GXM is very exotic)?
> 2. would we also implement this for the USB3 "pipes" as well (without
> being able to test this)?
> 3. from what I can see in the code we have to adjust dwc3_phy_setup()
> and ulpi.c to add support for multiple ports, but how do we detect the
> number of USB2 and USB3 ports (is this somewhere encoded in the
> DWC3_GHWPARAMS registers)?
> lsusb output is also attached, based on the PHY drivers for which the
> patches can be found here: [0]
> Best Regards,
> Martin
> [0] http://lists.infradead.org/pipermail/linux-amlogic/2016-November/001721.html
re-sending due to a typo in Felipe Balbi's email address (sorry for that)

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