Messages in this thread | | | Subject | Re: [PATCH v3 2/2] usb: host: ehci-tegra: Avoid getting the same reset twice | From | Stephen Warren <> | Date | Wed, 4 May 2016 11:23:20 -0600 |
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On 05/04/2016 08:40 AM, Thierry Reding wrote: > 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: ... > 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.
> diff --git 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)
> + 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;
Isn't that just:
has_utmi_pad_registers = of_property_read_bool(phy_np, "nvidia,has-utmi-pad-registers");
... and then you can remove " = false" from the declaration too?
> 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; ... > usb1_reset_attempted = true; > }
This is a pre-existing issue, but what happens if the probes for two USB controllers run in parallel; there seems to be missing locking related to testing/setting usb1_reset_attempted, which could cause multiple parallel attempts to get the "utmi-pads" reset object, which would presumably cause essentially the same issue this patch is solving in other cases?
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