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

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

Hi Roger,

On Tue, Oct 08, 2024, Roger Quadros wrote:
> Hi Thinh,
> 
> On 05/10/2024 04:04, Thinh Nguyen wrote:
> > 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:
> 
> Looking at this again, this fix is not specific to AM62 but for all platforms.
> e.g. if Host Role was already started when going to system suspend, SUSPHY bits
> were enabled, then after system resume SUSPHY bits are cleared at dwc3_core_init_for_resume().
> 
> Host stop/start was not called so SUSPHY bits remain cleared. So here
> we deal with enabling SUSPHY.
> 

It's true that we have a bug where the SUSPHY bits remain disabled after
suspend. However, the SUSPHY bits needing to be set during suspend is
unique to AM62. Let's add this note in the dwc3_suspend_common() check.

Thanks,
Thinh