Re: [PATCH v2 2/2] usb: dwc3: core: Add support to ignore single SE0 glitches

[AKASH KUMAR <quic_akakum@quicinc.com>]

Hi Uttkarsh, Thinh,

On 10/17/2024 5:10 PM, Uttkarsh Aggarwal wrote:
> Currently in few of Qualcomm chips USB (Low speed) mouse not
> detected showing following errors:
>
>    usb 1-1: Device not responding to setup address.
>    usb 1-1: device not accepting address 2, error -71
>    usb 1-1: new low-speed USB device number 3 using xhci-hcd
>    usb 1-1: Device not responding to setup address.
>    usb 1-1: Device not responding to setup address.
>    usb 1-1: device not accepting address 3, error -71
>    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.
>
> Signed-off-by: Uttkarsh Aggarwal<quic_uaggarwa@quicinc.com>
> ---
>   drivers/usb/dwc3/core.c | 13 +++++++++++++
>   drivers/usb/dwc3/core.h |  4 ++++
>   2 files changed, 17 insertions(+)
>
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 86b37881aab4..4edd32c44e73 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -222,6 +222,17 @@ 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.
> +		*/
> +		if (dwc->filter_se0_fsls_eop_quirk) {
> +			reg = dwc3_readl(dwc->regs, DWC3_GUCTL1);
> +			reg |= DWC3_GUCTL1_FILTER_SE0_FSLS_EOP;
> +			dwc3_writel(dwc->regs, DWC3_GUCTL1, reg);
> +		}
> +
Since this bit is useful for device mode as well along with host mode,we 
should set this in dwc3_core_init
where we are already writing for GUCTL1 bit disable parkmode, instead of 
host mode only. Like below

--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -1444,6 +1444,9 @@ static int dwc3_core_init(struct dwc3 *dwc)
                 if (dwc->parkmode_disable_hs_quirk)
                         reg |= DWC3_GUCTL1_PARKMODE_DISABLE_HS;

+               if (dwc->filter_se0_fsls_eop_quirk)
+                       reg |= DWC3_GUCTL1_FILTER_SE0_FSLS_EOP;
+
                 if (DWC3_VER_IS_WITHIN(DWC3, 290A, ANY)) {
                         if (dwc->maximum_speed == USB_SPEED_FULL ||
                             dwc->maximum_speed == USB_SPEED_HIGH)
>   		ret = dwc3_host_init(dwc);
>   		if (ret) {
>   			dev_err(dwc->dev, "failed to initialize host\n");
> @@ -1788,6 +1799,8 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>   
>   	dwc->tx_de_emphasis_quirk = device_property_read_bool(dev,
>   				"snps,tx_de_emphasis_quirk");
> +	dwc->filter_se0_fsls_eop_quirk = device_property_read_bool(dev,
> +				"snps,filter-se0-fsls-eop-quirk");
>   	device_property_read_u8(dev, "snps,tx_de_emphasis",
>   				&tx_de_emphasis);
>   	device_property_read_string(dev, "snps,hsphy_interface",
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index cc3f32acfaf5..33d53a436fd7 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -276,6 +276,7 @@
>   
>   /* Global User Control 1 Register */
>   #define DWC3_GUCTL1_DEV_DECOUPLE_L1L2_EVT	BIT(31)
> +#define DWC3_GUCTL1_FILTER_SE0_FSLS_EOP		BIT(29)
>   #define DWC3_GUCTL1_TX_IPGAP_LINECHECK_DIS	BIT(28)
>   #define DWC3_GUCTL1_DEV_FORCE_20_CLK_FOR_30_CLK	BIT(26)
>   #define DWC3_GUCTL1_DEV_L1_EXIT_BY_HW		BIT(24)
> @@ -1140,6 +1141,8 @@ struct dwc3_scratchpad_array {
>    * @gfladj_refclk_lpm_sel: set if we need to enable SOF/ITP counter
>    *                          running based on ref_clk
>    * @tx_de_emphasis_quirk: set if we enable Tx de-emphasis quirk
> + * @filter_se0_fsls_eop_quirk: set to ignores single
> + *				SE0 glitch on the linestate during transmit.
>    * @tx_de_emphasis: Tx de-emphasis value
>    *	0	- -6dB de-emphasis
>    *	1	- -3.5dB de-emphasis
> @@ -1373,6 +1376,7 @@ struct dwc3 {
>   	unsigned		gfladj_refclk_lpm_sel:1;
>   
>   	unsigned		tx_de_emphasis_quirk:1;
> +	unsigned		filter_se0_fsls_eop_quirk:1;
>   	unsigned		tx_de_emphasis:2;
>   
>   	unsigned		dis_metastability_quirk:1;

Thanks,
Akash