linux-kernel - Re: [PATCH v2, 3/3] usb: dwc3: core: Workaround for CSR read timeout

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Date: Fri, 7 Jun 2024 22:49:48 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: joswang <joswang1221@...il.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
        "conor+dt@...nel.org" <conor+dt@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        joswang <joswang@...ovo.com>
Subject: Re: [PATCH v2, 3/3] usb: dwc3: core: Workaround for CSR read timeout

On Fri, Jun 07, 2024, joswang wrote:

> My initial idea was similar to yours,Please help review the following changes.


> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 3a8fbc2d6b99..8c6a09718737 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -961,11 +961,15 @@ static bool dwc3_core_is_valid(struct dwc3 *dwc)
>  static void dwc3_core_setup_global_control(struct dwc3 *dwc)
>  {
>         u32 reg;
> +       unsigned int power_opt;
> +       unsigned int hw_mode;

Use reverse christmas tree declaration style:

	type1 abcdefg
	type2 abcde
	type3 abc

>  
>         reg = dwc3_readl(dwc->regs, DWC3_GCTL);
>         reg &= ~DWC3_GCTL_SCALEDOWN_MASK;
> +       hw_mode = DWC3_GHWPARAMS0_MODE(dwc->hwparams.hwparams0);
> +       power_opt = DWC3_GHWPARAMS1_EN_PWROPT(dwc->hwparams.hwparams1);
>  
> -       switch (DWC3_GHWPARAMS1_EN_PWROPT(dwc->hwparams.hwparams1)) {
> +       switch (power_opt) {
>         case DWC3_GHWPARAMS1_EN_PWROPT_CLK:
>                 /**
>                  * WORKAROUND: DWC3 revisions between 2.10a and 2.50a have an
> @@ -998,6 +1002,18 @@ static void dwc3_core_setup_global_control(struct dwc3
> *dwc)
>                 break;
>         }
>  
> +       /*
> +        * WORKAROUND: DWC_usb31 version 2.00a have an issue that would
> +        * cause a CSR read timeout When CSR read coincides with RAM
> +        * Clock Gating Entry.

Note in the comment and commit message that this applies while operating
as host mode. Add the STAR number reference in the commit message.

> +        *
> +        * This workaround solution disable Clock Gating, sacrificing
> +        * power consumption for normal operation.
> +        */
> +       if (power_opt != DWC3_GHWPARAMS1_EN_PWROPT_NO &&
> +           hw_mode != DWC3_GHWPARAMS0_MODE_GADGET && DWC3_VER_IS(DWC31, 200A))
> +               reg |= DWC3_GCTL_DSBLCLKGTNG;
> +

Thanks,
Thinh