Re: [PATCH v5 2/2] usb: dwc3: core: defer probe on ulpi_read_id timeout

[Thinh Nguyen]

On Mon, Dec 05, 2022, Ferry Toth wrote:
> Since commit 0f0101719138 ("usb: dwc3: Don't switch OTG -> peripheral
> if extcon is present"), Dual Role support on Intel Merrifield platform
> broke due to rearranging the call to dwc3_get_extcon().
> 
> It appears to be caused by ulpi_read_id() masking the timeout on the first
> test write. In the past dwc3 probe continued by calling dwc3_core_soft_reset()
> followed by dwc3_get_extcon() which happend to return -EPROBE_DEFER.
> On deferred probe ulpi_read_id() finally succeeded. Due to above mentioned
> rearranging -EPROBE_DEFER is not returned and probe completes without phy.
> 
> On Intel Merrifield the timeout on the first test write issue is reproducible
> but it is difficult to find the root cause. Using a mainline kernel and
> rootfs with buildroot ulpi_read_id() succeeds. As soon as adding
> ftrace / bootconfig to find out why, ulpi_read_id() fails and we can't
> analyze the flow. Using another rootfs ulpi_read_id() fails even without
> adding ftrace. We suspect the issue is some kind of timing / race, but
> merely retrying ulpi_read_id() does not resolve the issue.
> 
> As we now changed ulpi_read_id() to return -ETIMEDOUT in this case, we
> need to handle the error by calling dwc3_core_soft_reset() and request
> -EPROBE_DEFER. On deferred probe ulpi_read_id() is retried and succeeds.
> 
> Fixes: ef6a7bcfb01c ("usb: ulpi: Support device discovery via DT")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Ferry Toth <ftoth@xxxxxxxxxxxxxx>
> ---
>  drivers/usb/dwc3/core.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 648f1c570021..2779f17bffaf 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -1106,8 +1106,13 @@ static int dwc3_core_init(struct dwc3 *dwc)
>  
>  	if (!dwc->ulpi_ready) {
>  		ret = dwc3_core_ulpi_init(dwc);
> -		if (ret)
> +		if (ret) {
> +			if (ret == -ETIMEDOUT) {
> +				dwc3_core_soft_reset(dwc);
> +				ret = -EPROBE_DEFER;
> +			}
>  			goto err0;
> +		}
>  		dwc->ulpi_ready = true;
>  	}
>  
> -- 
> 2.37.2
> 

Acked-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>

Thanks,
Thinh