Re: [PATCH] usb: dwc3: core: Fix system suspend on TI AM62 platforms

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

Hi,

On Tue, Oct 01, 2024, Roger Quadros wrote:
> Since commit 6d735722063a ("usb: dwc3: core: Prevent phy suspend during init"),
> system suspend is broken on AM62 TI platforms.
> 
> Before that commit, both DWC3_GUSB3PIPECTL_SUSPHY and DWC3_GUSB2PHYCFG_SUSPHY
> bits (hence forth called 2 SUSPHY bits) were being set during core
> initialization and even during core re-initialization after a system
> suspend/resume.
> 
> These bits are required to be set for system suspend/resume to work correctly
> on AM62 platforms.
> 
> Since that commit, the 2 SUSPHY bits are not set for DEVICE/OTG mode if gadget
> driver is not loaded and started.
> For Host mode, the 2 SUSPHY bits are set before the first system suspend but
> get cleared at system resume during core re-init and are never set again.
> 
> This patch resovles these two issues by ensuring the 2 SUSPHY bits are set
> before system suspend and restored to the original state during system resume.
> 
> Cc: stable@vger.kernel.org # v6.9+
> Fixes: 6d735722063a ("usb: dwc3: core: Prevent phy suspend during init")
> Link: https://urldefense.com/v3/__https://lore.kernel.org/all/1519dbe7-73b6-4afc-bfe3-23f4f75d772f@kernel.org/__;!!A4F2R9G_pg!ahChm4MaKd6VGYqbnM4X1_pY_jqavYDv5HvPFbmicKuhvFsBwlEFi1xO5itGuHmfjbRuUSzReJISf5-1gXpr$ 
> Signed-off-by: Roger Quadros <rogerq@kernel.org>
> ---
>  drivers/usb/dwc3/core.c | 16 ++++++++++++++++
>  drivers/usb/dwc3/core.h |  2 ++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 9eb085f359ce..1233922d4d54 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -2336,6 +2336,9 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
>  	u32 reg;
>  	int i;
>  
> +	dwc->susphy_state = !!(dwc3_readl(dwc->regs, DWC3_GUSB2PHYCFG(0)) &
> +			    DWC3_GUSB2PHYCFG_SUSPHY);
> +
>  	switch (dwc->current_dr_role) {
>  	case DWC3_GCTL_PRTCAP_DEVICE:
>  		if (pm_runtime_suspended(dwc->dev))
> @@ -2387,6 +2390,11 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
>  		break;
>  	}
>  
> +	if (!PMSG_IS_AUTO(msg)) {
> +		if (!dwc->susphy_state)
> +			dwc3_enable_susphy(dwc, true);
> +	}
> +
>  	return 0;
>  }
>  
> @@ -2454,6 +2462,14 @@ static int dwc3_resume_common(struct dwc3 *dwc, pm_message_t msg)
>  		break;
>  	}
>  
> +	if (!PMSG_IS_AUTO(msg)) {
> +		/* dwc3_core_init_for_resume() disables SUSPHY so just handle
> +		 * the enable case
> +		 */

Can we note that this is a particular behavior needed for AM62 here?
And can we use this comment style:

/*
 * xxxxx
 * xxxxx
 */


> +		if (dwc->susphy_state)

Shouldn't we check for if (!dwc->susphy_state) and clear the susphy
bits?

> +			dwc3_enable_susphy(dwc, true);

The dwc3_enable_susphy() set and clear both GUSB3PIPECTL_SUSPHY and
GUSB2PHYCFG_SUSPHY, perhaps we should split that function out so we can
only need to set for GUSB2PHYCFG_SUSPHY since you only track for that.

> +	}
> +
>  	return 0;
>  }
>  
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index c71240e8f7c7..b2ed5aba4c72 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -1150,6 +1150,7 @@ struct dwc3_scratchpad_array {
>   * @sys_wakeup: set if the device may do system wakeup.
>   * @wakeup_configured: set if the device is configured for remote wakeup.
>   * @suspended: set to track suspend event due to U3/L2.
> + * @susphy_state: state of DWC3_GUSB2PHYCFG_SUSPHY before PM suspend.
>   * @imod_interval: set the interrupt moderation interval in 250ns
>   *			increments or 0 to disable.
>   * @max_cfg_eps: current max number of IN eps used across all USB configs.
> @@ -1382,6 +1383,7 @@ struct dwc3 {
>  	unsigned		sys_wakeup:1;
>  	unsigned		wakeup_configured:1;
>  	unsigned		suspended:1;
> +	unsigned		susphy_state:1;
>  
>  	u16			imod_interval;
>  
> 
> ---
> base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc
> change-id: 20240923-am62-lpm-usb-f420917bd707
> 
> Best regards,
> -- 
> Roger Quadros <rogerq@kernel.org>
> 

<rant/>
While reviewing your change, I see that we misuse the
dis_u2_susphy_quirk to make this property a conditional thing during
suspend and resume for certain platform. That bugs me because we can't
easily change it without the reported hardware to test.
</rant>

Thanks for the patch!

BR,
Thinh