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    SubjectRe: [PATCH v3 2/2] usb: host: ehci-tegra: Avoid getting the same reset twice
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    Hi Thierry,

    Am Mittwoch, den 04.05.2016, 16:40 +0200 schrieb Thierry Reding:
    > From: Thierry Reding <treding@nvidia.com>
    >
    > Starting with commit 0b52297f2288 ("reset: Add support for shared reset
    > controls") there is a reference count for reset control assertions. The
    > goal is to allow resets to be shared by multiple devices and an assert
    > will take effect only when all instances have asserted the reset.
    >
    > In order to preserve backwards-compatibility, all reset controls become
    > exclusive by default. This is to ensure that reset_control_assert() can
    > immediately assert in hardware.
    >
    > However, this new behaviour triggers the following warning in the EHCI
    > driver for Tegra:
    >
    > [ 3.365019] ------------[ cut here ]------------
    > [ 3.369639] WARNING: CPU: 0 PID: 1 at drivers/reset/core.c:187 __of_reset_control_get+0x16c/0x23c
    > [ 3.382151] Modules linked in:
    > [ 3.385214] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.6.0-rc6-next-20160503 #140
    > [ 3.392769] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
    > [ 3.399046] [<c010fa50>] (unwind_backtrace) from [<c010b120>] (show_stack+0x10/0x14)
    > [ 3.406787] [<c010b120>] (show_stack) from [<c0347dcc>] (dump_stack+0x90/0xa4)
    > [ 3.414007] [<c0347dcc>] (dump_stack) from [<c011f4fc>] (__warn+0xe8/0x100)
    > [ 3.420964] [<c011f4fc>] (__warn) from [<c011f5c4>] (warn_slowpath_null+0x20/0x28)
    > [ 3.428525] [<c011f5c4>] (warn_slowpath_null) from [<c03cc8cc>] (__of_reset_control_get+0x16c/0x23c)
    > [ 3.437648] [<c03cc8cc>] (__of_reset_control_get) from [<c0526858>] (tegra_ehci_probe+0x394/0x518)
    > [ 3.446600] [<c0526858>] (tegra_ehci_probe) from [<c04516d8>] (platform_drv_probe+0x4c/0xb0)
    > [ 3.455029] [<c04516d8>] (platform_drv_probe) from [<c044fe78>] (driver_probe_device+0x1ec/0x330)
    > [ 3.463892] [<c044fe78>] (driver_probe_device) from [<c0450074>] (__driver_attach+0xb8/0xbc)
    > [ 3.472320] [<c0450074>] (__driver_attach) from [<c044e1ec>] (bus_for_each_dev+0x68/0x9c)
    > [ 3.480489] [<c044e1ec>] (bus_for_each_dev) from [<c044f338>] (bus_add_driver+0x1a0/0x218)
    > [ 3.488743] [<c044f338>] (bus_add_driver) from [<c0450768>] (driver_register+0x78/0xf8)
    > [ 3.496738] [<c0450768>] (driver_register) from [<c010178c>] (do_one_initcall+0x40/0x170)
    > [ 3.504909] [<c010178c>] (do_one_initcall) from [<c0c00ddc>] (kernel_init_freeable+0x158/0x1f8)
    > [ 3.513600] [<c0c00ddc>] (kernel_init_freeable) from [<c0810784>] (kernel_init+0x8/0x114)
    > [ 3.521770] [<c0810784>] (kernel_init) from [<c0107778>] (ret_from_fork+0x14/0x3c)
    > [ 3.529361] ---[ end trace 4bda87dbe4ecef8a ]---
    >
    > The reason is that Tegra SoCs have three EHCI controllers, each with a
    > separate reset line. However the first controller contains UTMI pads
    > configuration registers that are shared with its siblings and that are
    > reset as part of the first controller's reset. There is special code in
    > the driver to assert and deassert this shared reset at probe time, and
    > it does so irrespective of which controller is probed first to ensure
    > that these shared registers are reset before any of the controllers are
    > initialized. Unfortunately this means that if the first controller gets
    > probed first, it will request its own reset line and will subsequently
    > request the same reset line again (temporarily) to perform the reset.
    > This used to work fine before the above-mentioned commit, but now
    > triggers the new WARN.
    >
    > Work around this by making sure we reuse the controller's reset if the
    > controller happens to be the first controller.
    >
    > Cc: Philipp Zabel <p.zabel@pengutronix.de>
    > Cc: Hans de Goede <hdegoede@redhat.com>
    > Signed-off-by: Thierry Reding <treding@nvidia.com>
    > ---
    > Changes in v3:
    > - reword commit message to more accurately describe the hardware design

    Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>

    > Changes in v2:
    > - restore has_utmi_pad_registers condition (Alan Stern)
    >
    > drivers/usb/host/ehci-tegra.c | 16 +++++++++++++---
    > 1 file changed, 13 insertions(+), 3 deletions(-)
    >
    > diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
    > index c1c1024a054c..8396b622f238 100644
    > --- a/drivers/usb/host/ehci-tegra.c
    > +++ b/drivers/usb/host/ehci-tegra.c
    > @@ -81,15 +81,23 @@ static int tegra_reset_usb_controller(struct platform_device *pdev)
    > struct usb_hcd *hcd = platform_get_drvdata(pdev);
    > struct tegra_ehci_hcd *tegra =
    > (struct tegra_ehci_hcd *)hcd_to_ehci(hcd)->priv;
    > + bool has_utmi_pad_registers = false;
    >
    > phy_np = of_parse_phandle(pdev->dev.of_node, "nvidia,phy", 0);
    > if (!phy_np)
    > return -ENOENT;
    >
    > + if (of_property_read_bool(phy_np, "nvidia,has-utmi-pad-registers"))
    > + has_utmi_pad_registers = true;
    > +
    > if (!usb1_reset_attempted) {
    > struct reset_control *usb1_reset;
    >
    > - usb1_reset = of_reset_control_get(phy_np, "utmi-pads");
    > + if (!has_utmi_pad_registers)
    > + usb1_reset = of_reset_control_get(phy_np, "utmi-pads");
    > + else
    > + usb1_reset = tegra->rst;
    > +
    > if (IS_ERR(usb1_reset)) {
    > dev_warn(&pdev->dev,
    > "can't get utmi-pads reset from the PHY\n");
    > @@ -101,11 +109,13 @@ static int tegra_reset_usb_controller(struct platform_device *pdev)
    > reset_control_deassert(usb1_reset);
    > }
    >
    > - reset_control_put(usb1_reset);
    > + if (!has_utmi_pad_registers)
    > + reset_control_put(usb1_reset);
    > +

    While you touch this, could you move the reset_control_put inside the
    (!IS_ERR(usb1_reset)) section above, maybe in a separate patch?

    We might start to warn in reset_control_put() if it is called with an
    error value as parameter in the future.

    > usb1_reset_attempted = true;
    > }
    >
    > - if (!of_property_read_bool(phy_np, "nvidia,has-utmi-pad-registers")) {
    > + if (!has_utmi_pad_registers) {
    > reset_control_assert(tegra->rst);
    > udelay(1);
    > reset_control_deassert(tegra->rst);

    regards
    Philipp

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