linux-kernel - Re: [PATCH v3 1/2] usb: host: ehci-tegra: Grab the correct UTMI pads reset

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Date:	Thu, 5 May 2016 08:39:25 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Thierry Reding <thierry.reding@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <gnurou@...il.com>,
	<linux-usb@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] usb: host: ehci-tegra: Grab the correct UTMI pads
 reset


On 04/05/16 15:39, Thierry Reding wrote:
> From: Thierry Reding <treding@...dia.com>
> 
> There are three EHCI controllers on Tegra SoCs, each with its own reset
> line. However, the first controller contains a set of UTMI configuration
> registers that are shared with its siblings. These registers will only
> be reset as part of the first controller's reset. For proper operation
> it must be ensured that the UTMI configuration registers are reset
> before any of the EHCI controllers are enabled, irrespective of the
> probe order.
> 
> Commit a47cc24cd1e5 ("USB: EHCI: tegra: Fix probe order issue leading to
> broken USB") introduced code that ensures the first controller is always
> reset before setting up any of the controllers, and is never again reset
> afterwards.
> 
> This code, however, grabs the wrong reset. Each EHCI controller has two
> reset controls attached: 1) the USB controller reset and 2) the UTMI
> pads reset (really the first controller's reset). In order to reset the
> UTMI pads registers the code must grab the second reset, but instead it
> grabbing the first.
> 
> Signed-off-by: Thierry Reding <treding@...dia.com>
> ---
> Stephen, Alex, Jon, have you ever encountered cases where UTMI might not
> have worked correctly? It seems that this code was pulsing the wrong
> reset line and therefore the UTMI pads would never be reset unless the
> first USB controller was probed before all others. I've never seen any
> such problems myself, so I'm unsure about whether it's worth Cc'ing the
> patch to stable@...r.kernel.org.
> 
>  drivers/usb/host/ehci-tegra.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
> index 4031b372008e..c1c1024a054c 100644
> --- a/drivers/usb/host/ehci-tegra.c
> +++ b/drivers/usb/host/ehci-tegra.c
> @@ -89,7 +89,7 @@ static int tegra_reset_usb_controller(struct platform_device *pdev)
>  	if (!usb1_reset_attempted) {
>  		struct reset_control *usb1_reset;
>  
> -		usb1_reset = of_reset_control_get(phy_np, "usb");
> +		usb1_reset = of_reset_control_get(phy_np, "utmi-pads");
>  		if (IS_ERR(usb1_reset)) {
>  			dev_warn(&pdev->dev,
>  				 "can't get utmi-pads reset from the PHY\n");
> 

I have not seen any issues either, but may be we were getting lucky. The
change makes sense to me.

Acked-by: Jon Hunter <jonathanh@...dia.com>

Cheers
Jon