linux-kernel - Re: [PATCH v2] usb: dwc3: core: set force_gen1 bit in USB31 devices if max speed is SS

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Message-ID: <20230517001105.v74dyo6asqtcrpii@synopsys.com>
Date:   Wed, 17 May 2023 00:11:12 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Krishna Kurapati <quic_kriskura@...cinc.com>
CC:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "quic_ppratap@...cinc.com" <quic_ppratap@...cinc.com>,
        "quic_wcheng@...cinc.com" <quic_wcheng@...cinc.com>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>,
        "quic_ugoswami@...cinc.com" <quic_ugoswami@...cinc.com>
Subject: Re: [PATCH v2] usb: dwc3: core: set force_gen1 bit in USB31 devices
 if max speed is SS

On Sun, May 14, 2023, Krishna Kurapati wrote:
> Currently for dwc3_usb31 controller, if maximum_speed is limited to
> super-speed in DT, then device mode is limited to SS, but host mode
> still works in SSP.
> 
> The documentation for max-speed property is as follows:
> 
> "Tells USB controllers we want to work up to a certain speed.
> Incase  this isn't passed via DT, USB controllers should default to
> their maximum HW capability."
> 
> It doesn't specify that the property is only for device mode.
> There are cases where we need to limit the host's maximum speed to
> SuperSpeed only. Use this property for host mode to contrain host's
> speed to SuperSpeed.
> 
> Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
> ---
> Link to v1: https://urldefense.com/v3/__https://lore.kernel.org/all/20230512170107.18821-1-quic_kriskura@quicinc.com/__;!!A4F2R9G_pg!dCg_3WK2oNXNb6d0a_VuyjkeeZJTU1aY4dik6g35XB7mtG7EJeR1uPMfxFja49OfXp7Yhsg1yqjnylCYYEg7YCAhqfAZ0Q$ 
> 
> Discussion regarding the same at:
> https://urldefense.com/v3/__https://lore.kernel.org/all/e465c69c-3a9d-cbdb-d44e-96b99cfa1a92@quicinc.com/__;!!A4F2R9G_pg!dCg_3WK2oNXNb6d0a_VuyjkeeZJTU1aY4dik6g35XB7mtG7EJeR1uPMfxFja49OfXp7Yhsg1yqjnylCYYEg7YCDRLUrJWg$ 
> 
>  drivers/usb/dwc3/core.c | 8 ++++++++
>  drivers/usb/dwc3/core.h | 5 +++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 278cd1c33841..33bc72595e74 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -1262,6 +1262,14 @@ static int dwc3_core_init(struct dwc3 *dwc)
>  		}
>  	}
>  
> +	if ((hw_mode != DWC3_GHWPARAMS0_MODE_GADGET) &&
> +	    (DWC3_IP_IS(DWC31)) &&
> +	    (dwc->maximum_speed == USB_SPEED_SUPER)) {
> +		reg = dwc3_readl(dwc->regs, DWC3_LLUCTL);
> +		reg |= DWC3_LLUCTL_FORCE_GEN1;
> +		dwc3_writel(dwc->regs, DWC3_LLUCTL, reg);
> +	}
> +

Perhaps this should be done for every usb3 port rather than just the
port_0. This patch can go after your multi-port series is added to
Greg's branch where you can check for number of usb3 ports.

Thanks,
Thinh

>  	return 0;
>  
>  err_power_off_phy:
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index 1968638f29ed..5a251da309d4 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -172,6 +172,8 @@
>  #define DWC3_OEVTEN		0xcc0C
>  #define DWC3_OSTS		0xcc10
>  
> +#define DWC3_LLUCTL		0xd024
> +
>  /* Bit fields */
>  
>  /* Global SoC Bus Configuration INCRx Register 0 */
> @@ -655,6 +657,9 @@
>  #define DWC3_OSTS_VBUSVLD		BIT(1)
>  #define DWC3_OSTS_CONIDSTS		BIT(0)
>  
> +/* Force Gen1 speed on Gen2 link */
> +#define DWC3_LLUCTL_FORCE_GEN1		BIT(10)
> +
>  /* Structures */
>  
>  struct dwc3_trb;
> -- 
> 2.40.0
>