Re: [PATCH v2 4/4] usb: dwc3: xilinx: Add support to program MMI USB TX deemphasis

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Tue, Mar 31, 2026, Radhey Shyam Pandey wrote:
> Introduces support for programming the 18-bit TX Deemphasis value that
> drives the pipe_TxDeemph signal, as defined in the PIPE4 specification.
> 
> The configured value is recommended by Synopsys and is intended for
> standard (non-compliance) operation. These Gen2 equalization settings
> have been validated through both internal and external compliance
> testing. By applying this setting, the stability of USB 3.2 enumeration
> is improved and now SuperSpeedPlus devices are consistently recognized as
> USB 3.2 Gen 2 by the MMI USB Host controller.
> 
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
> ---
> Changes for v2:
> - Don't use compatible check for deemphasis programming.
> - Rename property "snps,lcsr_tx_deemph" to "snps,lcsr-tx-deemph"
>   (hyphens per kernel convention).
> - Fix double space in LCSR_TX_DEEMPH register comment.
> - Add blank line between register offset define and "Bit fields" section.
> ---
>  drivers/usb/dwc3/core.c        | 17 +++++++++++++++++
>  drivers/usb/dwc3/core.h        |  8 ++++++++
>  drivers/usb/dwc3/dwc3-xilinx.c | 15 ++++++++++++---
>  3 files changed, 37 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 161a4d58b2ce..e678a53a90b3 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -646,6 +646,15 @@ static void dwc3_config_soc_bus(struct dwc3 *dwc)
>  		reg |= DWC3_GSBUSCFG0_REQINFO(dwc->gsbuscfg0_reqinfo);
>  		dwc3_writel(dwc, DWC3_GSBUSCFG0, reg);
>  	}
> +
> +	if (dwc->csr_tx_deemph_field_1 != DWC3_LCSR_TX_DEEMPH_UNSPECIFIED) {
> +		u32 reg;
> +
> +		reg = dwc3_readl(dwc, DWC3_LCSR_TX_DEEMPH);
> +		reg &= ~DWC3_LCSR_TX_DEEMPH_MASK(~0);
> +		reg |= DWC3_LCSR_TX_DEEMPH_MASK(dwc->csr_tx_deemph_field_1);
> +		dwc3_writel(dwc, DWC3_LCSR_TX_DEEMPH, reg);
> +	}
>  }
>  
>  static int dwc3_core_ulpi_init(struct dwc3 *dwc)
> @@ -1671,11 +1680,13 @@ static void dwc3_core_exit_mode(struct dwc3 *dwc)
>  static void dwc3_get_software_properties(struct dwc3 *dwc,
>  					 const struct dwc3_properties *properties)
>  {
> +	u32 csr_tx_deemph_field_1;
>  	struct device *tmpdev;
>  	u16 gsbuscfg0_reqinfo;
>  	int ret;
>  
>  	dwc->gsbuscfg0_reqinfo = DWC3_GSBUSCFG0_REQINFO_UNSPECIFIED;
> +	dwc->csr_tx_deemph_field_1 = DWC3_LCSR_TX_DEEMPH_UNSPECIFIED;
>  
>  	if (properties->gsbuscfg0_reqinfo !=
>  	    DWC3_GSBUSCFG0_REQINFO_UNSPECIFIED) {
> @@ -1693,6 +1704,12 @@ static void dwc3_get_software_properties(struct dwc3 *dwc,
>  					       &gsbuscfg0_reqinfo);
>  		if (!ret)
>  			dwc->gsbuscfg0_reqinfo = gsbuscfg0_reqinfo;
> +
> +		ret = device_property_read_u32(tmpdev,
> +					       "snps,lcsr-tx-deemph",
> +					       &csr_tx_deemph_field_1);
> +		if (!ret)
> +			dwc->csr_tx_deemph_field_1 = csr_tx_deemph_field_1;
>  	}
>  }
>  
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index a35b3db1f9f3..99874ad09730 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -181,6 +181,8 @@
>  
>  #define DWC3_LLUCTL(n)		(0xd024 + ((n) * 0x80))
>  
> +#define DWC3_LCSR_TX_DEEMPH	0xd060
> +

This should be DWC3_LCSR_TX_DEEMPH(n) where n is the USB3 port number

>  /* Bit fields */
>  
>  /* Global SoC Bus Configuration INCRx Register 0 */
> @@ -198,6 +200,10 @@
>  #define DWC3_GSBUSCFG0_REQINFO(n)	(((n) & 0xffff) << 16)
>  #define DWC3_GSBUSCFG0_REQINFO_UNSPECIFIED	0xffffffff
>  
> +/* LCSR_TX_DEEMPH Register: setting TX deemphasis used in normal operation in gen2 */
> +#define DWC3_LCSR_TX_DEEMPH_MASK(n)		((n) & 0x3ffff)
> +#define DWC3_LCSR_TX_DEEMPH_UNSPECIFIED		0xffffffff
> +
>  /* Global Debug LSP MUX Select */
>  #define DWC3_GDBGLSPMUX_ENDBC		BIT(15)	/* Host only */
>  #define DWC3_GDBGLSPMUX_HOSTSELECT(n)	((n) & 0x3fff)
> @@ -1180,6 +1186,7 @@ struct dwc3_glue_ops {
>   * @wakeup_pending_funcs: Indicates whether any interface has requested for
>   *			 function wakeup in bitmap format where bit position
>   *			 represents interface_id.
> + * @csr_tx_deemph_field_1: stores TX deemphasis used in Gen2 operation.

How do you plan to apply this for the case of multiple USB3 ports. Only
to the first USB3 port0 or all of them? Document how you want to handle
this.

>   */
>  struct dwc3 {
>  	struct work_struct	drd_work;
> @@ -1417,6 +1424,7 @@ struct dwc3 {
>  	struct dentry		*debug_root;
>  	u32			gsbuscfg0_reqinfo;
>  	u32			wakeup_pending_funcs;
> +	u32			csr_tx_deemph_field_1;
>  };
>  
>  #define INCRX_BURST_MODE 0
> diff --git a/drivers/usb/dwc3/dwc3-xilinx.c b/drivers/usb/dwc3/dwc3-xilinx.c
> index f2dee28bdc65..44008856ee73 100644
> --- a/drivers/usb/dwc3/dwc3-xilinx.c
> +++ b/drivers/usb/dwc3/dwc3-xilinx.c
> @@ -41,11 +41,13 @@
>  #define PIPE_CLK_SELECT				0
>  #define XLNX_USB_FPD_POWER_PRSNT		0x80
>  #define FPD_POWER_PRSNT_OPTION			BIT(0)
> +#define XLNX_MMI_USB_TX_DEEMPH_DEF		0x8c45
>  
>  struct dwc3_xlnx;
>  
>  struct dwc3_xlnx_config {
>  	int				(*pltfm_init)(struct dwc3_xlnx *data);
> +	u32				tx_deemph;
>  	bool				map_resource;
>  };
>  
> @@ -284,6 +286,7 @@ static const struct dwc3_xlnx_config versal_config = {
>  
>  static const struct dwc3_xlnx_config versal2_config = {
>  	.pltfm_init = dwc3_xlnx_init_versal2,
> +	.tx_deemph = XLNX_MMI_USB_TX_DEEMPH_DEF,
>  };
>  
>  static const struct of_device_id dwc3_xlnx_of_match[] = {
> @@ -303,10 +306,12 @@ static const struct of_device_id dwc3_xlnx_of_match[] = {
>  };
>  MODULE_DEVICE_TABLE(of, dwc3_xlnx_of_match);
>  
> -static int dwc3_set_swnode(struct device *dev)
> +static int dwc3_set_swnode(struct dwc3_xlnx *priv_data)
>  {
> +	struct device *dev = priv_data->dev;
> +	const struct dwc3_xlnx_config *config = priv_data->dwc3_config;
>  	struct device_node *np = dev->of_node, *dwc3_np;
> -	struct property_entry props[2];
> +	struct property_entry props[3];
>  	int prop_idx = 0, ret = 0;
>  
>  	dwc3_np = of_get_compatible_child(np, "snps,dwc3");
> @@ -320,6 +325,10 @@ static int dwc3_set_swnode(struct device *dev)
>  	if (of_dma_is_coherent(dwc3_np))
>  		props[prop_idx++] = PROPERTY_ENTRY_U16("snps,gsbuscfg0-reqinfo",
>  						       0xffff);
> +	if (config->tx_deemph)

We should set the tx_deemph to the DWC3_LCSR_TX_DEEMPH_UNSPECIFIED by
default and check against that instead.

> +		props[prop_idx++] = PROPERTY_ENTRY_U32("snps,lcsr-tx-deemph",
> +						       config->tx_deemph);
> +
>  	of_node_put(dwc3_np);
>  
>  	if (prop_idx)
> @@ -368,7 +377,7 @@ static int dwc3_xlnx_probe(struct platform_device *pdev)
>  	if (ret)
>  		goto err_clk_put;
>  
> -	ret = dwc3_set_swnode(dev);
> +	ret = dwc3_set_swnode(priv_data);
>  	if (ret)
>  		goto err_clk_put;
>  
> -- 
> 2.43.0
> 

BR,
Thinh