[PATCH V4] usb: ehci-mx6: Enable OTG detection on imx8mm and imx8mn

[Adam Ford]

On Mon, Feb 7, 2022 at 2:47 AM Marek Vasut <marex at denx.de> wrote:
>
> On 2/7/22 01:51, Adam Ford wrote:
> > On Sun, Feb 6, 2022 at 3:59 PM Marek Vasut <marex at denx.de> wrote:
> >>
> >> On 2/3/22 22:20, Adam Ford wrote:
> >>> The imx8mm and imx8mn appear compatible with imx7d-usb
> >>> flags in the OTG driver.  If the dr_mode is defined as
> >>> host or peripheral, the device appears to operate correctly,
> >>> however the auto host/peripheral detection results in an error.
> >>>
> >>> The solution isn't just adding checks for imx8mm and imx8mn to
> >>> the check for imx7, because the USB clock needs to be running
> >>> to read from the USBNC_PHY_STATUS_OFFSET register or it will hang.
> >>>
> >>> Marek requested that I not enable the clocks in ehci_usb_of_to_plat,
> >>> so I modified that function to return an unknown state if the
> >>> device tree does not explicitly state whether it is a host
> >>> or a peripheral.
> >>>
> >>> When the driver probes, it looks to see if it's in the unknown
> >>> state, and only then will it read the register to auto-detect.
> >>>
> >>> Signed-off-by: Adam Ford <aford173 at gmail.com>
> >>> Tested-by: Tim Harvey <tharvey at gateworks.com>
> >>> ---
> >>> V4:  Fix 'err_clk' reference, so it is not encapsulated in
> >>>        an ifdef making it available at all times.
> >>> V3:  Keep ehci_usb_of_to_plat but add the ability to return
> >>>        and unknown state instead of reading the register.
> >>>        If the probe determines the states is unknown, it will
> >>>        query the register after the clocks have been enabled.
> >>>        Because of the slight behavior change, I removed any
> >>>        review or tested tags.
> >>>
> >>> V2:  Rename ehci_usb_of_to_plat to ehci_usb_dr_mode and call it
> >>>        from the probe after t
> >>>
> >>> diff --git a/drivers/usb/host/ehci-mx6.c b/drivers/usb/host/ehci-mx6.c
> >>> index 1bd6147c76..060b02accc 100644
> >>> --- a/drivers/usb/host/ehci-mx6.c
> >>> +++ b/drivers/usb/host/ehci-mx6.c
> >>> @@ -543,7 +543,7 @@ static int ehci_usb_phy_mode(struct udevice *dev)
> >>>                        plat->init_type = USB_INIT_DEVICE;
> >>>                else
> >>>                        plat->init_type = USB_INIT_HOST;
> >>> -     } else if (is_mx7()) {
> >>> +     } else if (is_mx7() || is_imx8mm() || is_imx8mn()) {
> >>>                phy_status = (void __iomem *)(addr +
> >>>                                              USBNC_PHY_STATUS_OFFSET);
> >>>                val = readl(phy_status);
> >>
> >> Is the USB GPCv2 power domain always ON at this point ? If it isn't,
> >> then this access will lock up the whole SoC.
> >
> > The GPCv2 needs to be enabled if USB is going to be used, but I would
> > expect that to happen even without this patch.  I ran into that during
> > my early testing.
> >
> >>
> >> You can check that easily by adding printf() into
> >> drivers/power/domain/imx8m-power-domain.c imx8m_power_domain_on() , and
> >> verify that printf() prints something before this ehci_usb_phy_mode()
> >> code is called.
> >
> > I added a printf to show when a power domain is enabled.  It does
> > appear that power domains for HSIO, USBOTG1 and USBOTG2 are all
> > enabled before the scan on the respective USB bus happens, so I think
> > we're safe from hanging.
>
> Isn't the ehci_usb_of_to_plat() called way before you even initiate the
> scan, somewhere during U-Boot startup ? So no, you might end up hanging
> the hardware ?

If you look at what this patch is doing, ehci_usb_of_to_plat is no
longer making any calls to the USB registers.  ehci_usb_of_to_plat is
just an exercise in reading the device tree for the desired mode.  If
it's not host mode or peripheral mode it returns unknown.  The part
that reads the registers now is delayed until after the clocks are
enabled inside the probe function which is called when USB is started
and the power-domains are available.

adam

>
> (you can verify that by adding more printf()s)