linux-kernel - Re: [PATCH v2 2/4] usb: uhci: Add reset control support

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Message-ID: <291b2bc2-6a61-44e9-91cb-56044c4277e6@rowland.harvard.edu>
Date: Wed, 17 Sep 2025 10:02:52 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Ryan Chen <ryan_chen@...eedtech.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Philipp Zabel <p.zabel@...gutronix.de>, linux-usb@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] usb: uhci: Add reset control support

On Wed, Sep 17, 2025 at 10:19:24AM +0800, Ryan Chen wrote:
> Some SoCs, such as the Aspeed AST2700, require the UHCI controller
> to be taken out of reset before it can operate. Add optional reset
> control support to the UHCI platform driver.
> 
> The driver now acquires an optional reset line from device tree,
> deasserts it during probe, and asserts it again in the error path
> and shutdown.
> 
> Signed-off-by: Ryan Chen <ryan_chen@...eedtech.com>
> ---
>  drivers/usb/host/uhci-hcd.h      |  1 +
>  drivers/usb/host/uhci-platform.c | 17 +++++++++++++++--
>  2 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/host/uhci-hcd.h b/drivers/usb/host/uhci-hcd.h
> index 13ee2a6144b2..4326d1f3ca76 100644
> --- a/drivers/usb/host/uhci-hcd.h
> +++ b/drivers/usb/host/uhci-hcd.h
> @@ -445,6 +445,7 @@ struct uhci_hcd {
>  	short load[MAX_PHASE];			/* Periodic allocations */
>  
>  	struct clk *clk;			/* (optional) clock source */
> +	struct reset_control *rsts;		/* (optional) clock reset */

This new field is used only in uhci_hcd_platform_probe().  Therefore it 
does not need to be stored in the uhci_hcd structure; it can simply be a 
local variable.

Alan Stern

>  
>  	/* Reset host controller */
>  	void	(*reset_hc) (struct uhci_hcd *uhci);
> diff --git a/drivers/usb/host/uhci-platform.c b/drivers/usb/host/uhci-platform.c
> index 62318291f566..1c1715bddc27 100644
> --- a/drivers/usb/host/uhci-platform.c
> +++ b/drivers/usb/host/uhci-platform.c
> @@ -11,6 +11,7 @@
>  #include <linux/of.h>
>  #include <linux/device.h>
>  #include <linux/platform_device.h>
> +#include <linux/reset.h>
>  
>  static int uhci_platform_init(struct usb_hcd *hcd)
>  {
> @@ -132,17 +133,29 @@ static int uhci_hcd_platform_probe(struct platform_device *pdev)
>  		goto err_rmr;
>  	}
>  
> +	uhci->rsts = devm_reset_control_array_get_optional_shared(&pdev->dev);
> +	if (IS_ERR(uhci->rsts)) {
> +		ret = PTR_ERR(uhci->rsts);
> +		goto err_clk;
> +	}
> +	ret = reset_control_deassert(uhci->rsts);
> +	if (ret)
> +		goto err_clk;
> +
>  	ret = platform_get_irq(pdev, 0);
>  	if (ret < 0)
> -		goto err_clk;
> +		goto err_reset;
>  
>  	ret = usb_add_hcd(hcd, ret, IRQF_SHARED);
>  	if (ret)
> -		goto err_clk;
> +		goto err_reset;
>  
>  	device_wakeup_enable(hcd->self.controller);
>  	return 0;
>  
> +err_reset:
> +	if (!IS_ERR_OR_NULL(uhci->rsts))
> +		reset_control_assert(uhci->rsts);
>  err_clk:
>  	clk_disable_unprepare(uhci->clk);
>  err_rmr:
> -- 
> 2.34.1
>