linux-kernel - Re: [PATCH] usb: dwc2: Skip clock gating on Samsung SoCs

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Message-ID: <a7efdf13-48bb-db21-5755-ebbbe2614f78@synopsys.com>
Date:   Fri, 16 Jul 2021 14:54:10 +0000
From:   Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Artur Petrosyan <Arthur.Petrosyan@...opsys.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH] usb: dwc2: Skip clock gating on Samsung SoCs

Hi Marek,

On 7/16/2021 9:01 AM, Marek Szyprowski wrote:
> Commit 0112b7ce68ea ("usb: dwc2: Update dwc2_handle_usb_suspend_intr
> function.") changed the way the driver handles power down modes in a such
> way that it uses clock gating when no other power down mode is available.
> 
> This however doesn't work well on the DWC2 implementation used on the
> Samsung SoCs. When a clock gating is enabled, system hangs. It looks that
> the proper clock gating requires some additional glue code in the shared
> USB2 PHY and/or Samsung glue code for the DWC2. To restore driver
> operation on the Samsung SoCs simply skip enabling clock gating mode
> until one finds what is really needed to make it working reliably.
> 
> Fixes: 0112b7ce68ea ("usb: dwc2: Update dwc2_handle_usb_suspend_intr function.")
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>   drivers/usb/dwc2/core.h      | 4 ++++
>   drivers/usb/dwc2/core_intr.c | 3 ++-
>   drivers/usb/dwc2/hcd.c       | 6 ++++--
>   drivers/usb/dwc2/params.c    | 1 +
>   4 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/dwc2/core.h b/drivers/usb/dwc2/core.h
> index ab6b815e0089..483de2bbfaab 100644
> --- a/drivers/usb/dwc2/core.h
> +++ b/drivers/usb/dwc2/core.h
> @@ -383,6 +383,9 @@ enum dwc2_ep0_state {
>    *			0 - No (default)
>    *			1 - Partial power down
>    *			2 - Hibernation
> + * @no_clock_gating:	Specifies whether to avoid clock gating feature.
> + *			0 - No (use clock gating)
> + *			1 - Yes (avoid it)
>    * @lpm:		Enable LPM support.
>    *			0 - No
>    *			1 - Yes
> @@ -480,6 +483,7 @@ struct dwc2_core_params {
>   #define DWC2_POWER_DOWN_PARAM_NONE		0
>   #define DWC2_POWER_DOWN_PARAM_PARTIAL		1
>   #define DWC2_POWER_DOWN_PARAM_HIBERNATION	2
> +	bool no_clock_gating;
>   
>   	bool lpm;
>   	bool lpm_clock_gating;
> diff --git a/drivers/usb/dwc2/core_intr.c b/drivers/usb/dwc2/core_intr.c
> index a5ab03808da6..a5c52b237e72 100644
> --- a/drivers/usb/dwc2/core_intr.c
> +++ b/drivers/usb/dwc2/core_intr.c
> @@ -556,7 +556,8 @@ static void dwc2_handle_usb_suspend_intr(struct dwc2_hsotg *hsotg)
>   				 * If neither hibernation nor partial power down are supported,
>   				 * clock gating is used to save power.
>   				 */
> -				dwc2_gadget_enter_clock_gating(hsotg);
> +				if (!hsotg->params.no_clock_gating)
> +					dwc2_gadget_enter_clock_gating(hsotg);
>   			}
>   
>   			/*
> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
> index 035d4911a3c3..2a7828971d05 100644
> --- a/drivers/usb/dwc2/hcd.c
> +++ b/drivers/usb/dwc2/hcd.c
> @@ -3338,7 +3338,8 @@ int dwc2_port_suspend(struct dwc2_hsotg *hsotg, u16 windex)
>   		 * If not hibernation nor partial power down are supported,
>   		 * clock gating is used to save power.
>   		 */
> -		dwc2_host_enter_clock_gating(hsotg);
> +		if (!hsotg->params.no_clock_gating)
> +			dwc2_host_enter_clock_gating(hsotg);
>   		break;
>   	}
>   
> @@ -4402,7 +4403,8 @@ static int _dwc2_hcd_suspend(struct usb_hcd *hcd)
>   		 * If not hibernation nor partial power down are supported,
>   		 * clock gating is used to save power.
>   		 */
> -		dwc2_host_enter_clock_gating(hsotg);
> +		if (!hsotg->params.no_clock_gating)
> +			dwc2_host_enter_clock_gating(hsotg);
>   
>   		/* After entering suspend, hardware is not accessible */
>   		clear_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags);
> diff --git a/drivers/usb/dwc2/params.c b/drivers/usb/dwc2/params.c
> index 67c5eb140232..59e119345994 100644
> --- a/drivers/usb/dwc2/params.c
> +++ b/drivers/usb/dwc2/params.c
> @@ -76,6 +76,7 @@ static void dwc2_set_s3c6400_params(struct dwc2_hsotg *hsotg)
>   	struct dwc2_core_params *p = &hsotg->params;
>   
>   	p->power_down = DWC2_POWER_DOWN_PARAM_NONE;
> +	p->no_clock_gating = true;
>   	p->phy_utmi_width = 8;
>   }
>   
> 
In which mode host/device you see the issue?
What is your core version? Please provide GHWCFG1-4 registers values.
Is the issue seen because of programming PCGCTL.PCGCTL_GATEHCLK bit 
only? To check it, could you please comment this bit setting/resetting 
in clock gating functions:
dwc2_host_exit_clock_gating()
dwc2_host_enter_clock_gating()
dwc2_gadget_exit_clock_gating()
dwc2_gadget_enter_clock_gating()

Thanks,
Minas