Re: [PATCH] usb: dwc3: qcom: Restore UTMI PIPE clock on resume

[Prashanth K <prashanth.k@oss.qualcomm.com>]

On 10/27/2026 6:51 AM, Filippo Falezza wrote:
> Boards whose controller has no SuperSpeed PHY set
> qcom,select-utmi-as-pipe-clk, and the glue then programs QSCRATCH
> GENERAL_CFG so that the core's PIPE clock domain runs from the UTMI
> clock. This is only done at probe.
> 
> When the SoC reaches its deepest state in suspend-to-idle (CX power
> collapse), the QSCRATCH registers lose their contents. On resume the
> core is reinitialised with its PIPE domain unclocked, and the gadget
> does not come back:
> 
>   dwc3-qcom a600000.usb: failed to enable ep0out
> 
> The link stays down until the driver is unbound and bound again.
> 
> Remember the property at probe and select the UTMI clock again in
> dwc3_qcom_resume(), after the clocks and interconnect paths are enabled
> and before the core is resumed. Move dwc3_qcom_select_utmi_clk() up so
> that it is defined before its new caller.
> 
> Fixes: a4333c3a6ba9 ("usb: dwc3: Add Qualcomm DWC3 glue driver")
> Signed-off-by: Filippo Falezza <effeffe99@gmail.com>
> ---
> Hello there,
> 
> this fixes USB peripheral mode after suspend on a Motorola Moto G 5G
> Plus (SM7250), a phone with a USB 2.0-only port that I'm bringing up on
> mainline. Its controller needs qcom,select-utmi-as-pipe-clk. The first
> s2idle that reached CX power collapse broke the gadget: "failed to
> enable ep0out" on resume, and USB networking stayed down until I
> rebound dwc3-qcom by hand. Rebinding works because probe programs
> GENERAL_CFG again, which is what this patch does in the resume path.
> 
> With the patch, the gadget (NCM plus ACM) reconnects after s2idle, and
> the SSH session over the cable that I use for testing survives
> suspend; the phone has run with it on linux-next since 11 October.
> The other boards that use
> qcom,select-utmi-as-pipe-clk should benefit as well, but I have only
> tested this one, in peripheral mode. The legacy glue driver
> (dwc3-qcom-legacy.c) has the same probe-only programming; I left it
> alone because I can't test it.
> 
> The patch is on top of usb-linus (6b4b543fa187) and builds with W=1 for
> arm64.
> 
> I wrote this patch and drafted this note with the help of an AI coding
> assistant (Claude Code). The testing above is on the phone.
> 

The patch looks good to me, did you test this with host mode and RT
suspend/resume?

> Thanks,
> Filippo
> ---
>  drivers/usb/dwc3/dwc3-qcom.c | 45 +++++++++++++++++++++++++++-----------------
>  1 file changed, 28 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index ac68b4218b56..6334ca7ba30f 100644
> --- a/drivers/usb/dwc3/dwc3-qcom.c
> +++ b/drivers/usb/dwc3/dwc3-qcom.c
> @@ -81,6 +81,7 @@ struct dwc3_qcom {
>  	enum usb_dr_mode	mode;
>  	bool			is_suspended;
>  	bool			pm_suspended;
> +	bool			utmi_as_pipe_clk;
>  	struct icc_path		*icc_path_ddr;
>  	struct icc_path		*icc_path_apps;
>  
> @@ -335,6 +336,23 @@ static void dwc3_qcom_enable_interrupts(struct dwc3_qcom *qcom)
>  		dwc3_qcom_enable_port_interrupts(&qcom->ports[i]);
>  }
>  
> +static void dwc3_qcom_select_utmi_clk(struct dwc3_qcom *qcom)
> +{
> +	/* Configure dwc3 to use UTMI clock as PIPE clock not present */
> +	dwc3_qcom_setbits(qcom->qscratch_base, QSCRATCH_GENERAL_CFG,
> +			  PIPE_UTMI_CLK_DIS);
> +
> +	usleep_range(100, 1000);
> +
> +	dwc3_qcom_setbits(qcom->qscratch_base, QSCRATCH_GENERAL_CFG,
> +			  PIPE_UTMI_CLK_SEL | PIPE3_PHYSTATUS_SW);
> +
> +	usleep_range(100, 1000);
> +
> +	dwc3_qcom_clrbits(qcom->qscratch_base, QSCRATCH_GENERAL_CFG,
> +			  PIPE_UTMI_CLK_DIS);
> +}
> +
>  static int dwc3_qcom_suspend(struct dwc3_qcom *qcom, bool wakeup)
>  {
>  	u32 val;
> @@ -388,6 +406,15 @@ static int dwc3_qcom_resume(struct dwc3_qcom *qcom, bool wakeup)
>  	if (ret)
>  		dev_warn(qcom->dev, "failed to enable interconnect: %d\n", ret);
>  
> +	/*
> +	 * The QSCRATCH registers lose their state when the controller's power
> +	 * domain is collapsed during system suspend: select the UTMI clock
> +	 * for the PIPE domain again, or the core can't run without a PIPE
> +	 * clock ("failed to enable ep0out").
> +	 */
> +	if (qcom->utmi_as_pipe_clk)
> +		dwc3_qcom_select_utmi_clk(qcom);
> +
>  	/* Clear existing events from PHY related to L2 in/out */
>  	for (i = 0; i < qcom->num_ports; i++) {
>  		dwc3_qcom_setbits(qcom->qscratch_base,
> @@ -419,23 +446,6 @@ static irqreturn_t qcom_dwc3_resume_irq(int irq, void *data)
>  	return IRQ_HANDLED;
>  }
>  
> -static void dwc3_qcom_select_utmi_clk(struct dwc3_qcom *qcom)
> -{
> -	/* Configure dwc3 to use UTMI clock as PIPE clock not present */
> -	dwc3_qcom_setbits(qcom->qscratch_base, QSCRATCH_GENERAL_CFG,
> -			  PIPE_UTMI_CLK_DIS);
> -
> -	usleep_range(100, 1000);
> -
> -	dwc3_qcom_setbits(qcom->qscratch_base, QSCRATCH_GENERAL_CFG,
> -			  PIPE_UTMI_CLK_SEL | PIPE3_PHYSTATUS_SW);
> -
> -	usleep_range(100, 1000);
> -
> -	dwc3_qcom_clrbits(qcom->qscratch_base, QSCRATCH_GENERAL_CFG,
> -			  PIPE_UTMI_CLK_DIS);
> -}
> -
>  static int dwc3_qcom_request_irq(struct dwc3_qcom *qcom, int irq,
>  				 const char *name)
>  {
> @@ -680,6 +690,7 @@ static int dwc3_qcom_probe(struct platform_device *pdev)
>  	 */
>  	ignore_pipe_clk = device_property_read_bool(dev,
>  				"qcom,select-utmi-as-pipe-clk");

Minor nit, You can use directly qcom->utmi_as_pipe_clk instead of
ignore_pipe_clk.

> +	qcom->utmi_as_pipe_clk = ignore_pipe_clk;
>  	if (ignore_pipe_clk)
>  		dwc3_qcom_select_utmi_clk(qcom);
>  
> 
> ---
> base-commit: 6b4b543fa18757297ac756a6fe6e64f506b7844a
> change-id: 20261027-dwc3-utmi-resume-5ff551b1ed1d
> 
> Best regards,
> --  
> Filippo Falezza <effeffe99@gmail.com>