linux-kernel - Re: [PATCH v1 2/2] usb: tegra: Move UTMI-pads reset from ehci-tegra to tegra-phy

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Message-ID: <20171211102523.GH10671@ulmo>
Date:   Mon, 11 Dec 2017 11:25:23 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-usb@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] usb: tegra: Move UTMI-pads reset from ehci-tegra
 to tegra-phy

On Mon, Dec 11, 2017 at 02:07:38AM +0300, Dmitry Osipenko wrote:
> UTMI pads are shared by USB controllers and reset of UTMI pads is shared
> with the reset of USB1 controller. Currently reset of UTMI pads is done by
> the EHCI driver and ChipIdea UDC works because EHCI driver always happen
> to be probed first. Move reset controls from ehci-tegra to tegra-phy in
> order to resolve the problem.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/usb/host/ehci-tegra.c     | 87 ++++++++++++++++++---------------------
>  drivers/usb/phy/phy-tegra-usb.c   | 46 +++++++++++++++++++++
>  include/linux/usb/tegra_usb_phy.h |  2 +
>  3 files changed, 87 insertions(+), 48 deletions(-)

I don't think we can do this. For one I don't think shared resets are
going to work here because you really won't ever be able to reset after
two devices have requested the same reset. Second, utmip_pad_close()
could be called at any point and it will have the side-effect of either
not doing a reset at all (because it is shared) or resetting the USBD
controller at the same time.

We've been over this code a great deal over the years. I'd love it to be
simpler, but every time we tried to simplify it, things broke.

Thierry

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