linux-kernel - Re: [PATCH] usb: dwc3: core: Set GUCTL1[29] to ignore single SE0 glitch for FS/LS operation

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Message-ID: <20240828021058.dxzzvrdqat4gwut2@synopsys.com>
Date: Wed, 28 Aug 2024 02:11:01 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: core: Set GUCTL1[29] to ignore single SE0
 glitch for FS/LS operation

On Fri, Aug 23, 2024, Uttkarsh Aggarwal wrote:
> Currently in few of Qualcomm chips USB LS mouse not detected
> showing following errors:
> 
> [ 81.585361] usb 1-1: Device not responding to setup address.
> [ 81.798676] usb 1-1: device not accepting address 2, error -71
> [ 81.928378] usb 1-1: new low-speed USB device number 3 using xhci-hcd
> [ 82.076248] usb 1-1: Device not responding to setup address.
> [ 82.290630] usb 1-1: Device not responding to setup address.
> [ 82.503877] usb 1-1: device not accepting address 3, error -71
> [ 82.512548] usb usb1-port1: attempt power cycle
> 
> Based on the Logic analyzer waveforms, It has been identified that
> there is skew of about 8nS b/w DP & DM linestate signals
> (o/p of PHY & i/p to controller) at the UTMI interface,
> Due to this controller is seeing SE0 glitch condition,
> this is causing controller to pre-maturely assume that PHY
> has sent all the data & is initiating next packet much early,
> though in reality PHY is still busy sending previous packets.
> 
> Enabling the GUCTL1.FILTER_SE0_FSLS_EOP bit29 allows the controller
> to ignore single SE0 glitches on the linestate during transmission.
> Only two or more SE0 signals are recognized as a valid EOP.
> 
> When this feature is activated, SE0 signals on the linestate
> are validated over two consecutive UTMI/ULPI clock edges for EOP detection.
> 
> Device mode (FS): If GUCTL1.FILTER_SE0_FSLS_EOP is set,
> then for device LPM handshake, the controller ignores single
> SE0 glitch on the linestate during transmit. Only two or more
> SE0 is considered as a valid EOP on FS port.
> 
> Host mode (FS/LS): If GUCTL1.FILTER_SE0_FSLS_EOP is set, then
> the controller ignores single SE0 glitch on the linestate during transmit.
> Only two or more SE0 is considered as a valid EOP on FS/LS port.
> 
> Signed-off-by: Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>
> ---
>  drivers/usb/dwc3/core.c | 10 ++++++++++
>  drivers/usb/dwc3/core.h |  1 +
>  2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 3e55838c0001..1edb16d2940c 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -194,6 +194,16 @@ static void __dwc3_set_mode(struct work_struct *work)
>  
>  	switch (desired_dr_role) {
>  	case DWC3_GCTL_PRTCAP_HOST:
> +
> +		/*
> +		 * Setting GUCTL1 bit 29 so that controller
> +		 * will ignore single SE0 glitch on the linestate
> +		 * during transmit.
> +		 */
> +		reg = dwc3_readl(dwc->regs, DWC3_GUCTL1);
> +		reg |= DWC3_GUCTL1_FILTER_SE0_FSLS_EOP;
> +		dwc3_writel(dwc->regs, DWC3_GUCTL1, reg);
> +
>  		ret = dwc3_host_init(dwc);
>  		if (ret) {
>  			dev_err(dwc->dev, "failed to initialize host\n");
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index e3eea965e57b..73e90daafecf 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -271,6 +271,7 @@
>  #define DWC3_GUCTL1_PARKMODE_DISABLE_SS		BIT(17)
>  #define DWC3_GUCTL1_PARKMODE_DISABLE_HS		BIT(16)
>  #define DWC3_GUCTL1_RESUME_OPMODE_HS_HOST	BIT(10)
> +#define DWC3_GUCTL1_FILTER_SE0_FSLS_EOP		BIT(29)
>  
>  /* Global Status Register */
>  #define DWC3_GSTS_OTG_IP	BIT(10)
> -- 
> 2.17.1
> 

This is your platform specific quirk. Please add proper checks to target
your platform only.

Thanks,
Thinh