Re: [PATCH V2] usb: phy: tegra: Fix phy suspend for UDC

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Mon, Oct 02, 2017 at 12:22:53PM +0100, Jon Hunter wrote:
> Commit dfebb5f43a78 ("usb: chipidea: Add support for Tegra20/30/114/124")
> added UDC support for Tegra but with UDC support enabled, is was found
> that Tegra30, Tegra114 and Tegra124 would hang on entry to suspend.
> 
> The hang occurred during the suspend of the USB PHY when the Tegra PHY
> driver attempted to disable the PHY clock. The problem is that before
> the Tegra PHY driver is suspended, the chipidea driver already disabled
> the PHY clock and when the Tegra PHY driver suspended, it could not read
> DEVLC register and caused the device to hang.
> 
> The Tegra USB PHY driver is used by both the Tegra EHCI driver and now
> the chipidea UDC driver and so simply removing the disabling of the PHY
> clock from the USB PHY driver would not work for the Tegra EHCI driver.
> Fortunately, the status of the USB PHY clock can be read from the
> USB_SUSP_CTRL register and therefore, to workaround this issue, simply
> poll the register prior to disabling the clock in USB PHY driver to see
> if clock gating has already been initiated. Please note that it can take
> a few uS for the clock to disable and so simply reading this status
> register once on entry is not sufficient.
> 
> Similarly when turning on the PHY clock, it is possible that the clock
> is already enabled or in the process of being enabled, and so check for
> this when enabling the PHY.
> 
> Please note that no issues are seen with Tegra20 because it has a slightly
> different PHY to Tegra30/114/124.
> 
> Fixes: dfebb5f43a78 ("usb: chipidea: Add support for Tegra20/30/114/124")
> 
> Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> ---
> Changes since V1:
> - Added fixes tag
> - Added test in PHY enable to see if clock is already on before enabling
> 
>  drivers/usb/phy/phy-tegra-usb.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)

Acked-by: Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>

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