Re: [PATCH 2/3] usb: dwc3: Add role switch relay support

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Sat 03 Jul 20:33 CDT 2021, Bryan O'Donoghue wrote:

> Add the ability to relay a role switch message from the core to the parent
> device of the controller.
> 
> This is useful for the qcom-dwc3 wrapper which wants to receive role-switch
> notifications in order to waggle internal SoC UTMI signals.
> 
> Having the core trigger the parent wrapper has the advantage of keeping the
> connector mechanism agnostic from dwc3 wrapper code and means that any
> other wrapper implementation on any other SoC or architecture need not
> write custom code to find various types of Type-C role switch mechanisms.
> 
> Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
> ---
>  drivers/usb/dwc3/core.h |  2 ++
>  drivers/usb/dwc3/drd.c  | 10 ++++++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index dccdf13b5f9e..974104cc16f7 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -993,6 +993,7 @@ struct dwc3_scratchpad_array {
>   *		- USBPHY_INTERFACE_MODE_UTMI
>   *		- USBPHY_INTERFACE_MODE_UTMIW
>   * @role_sw: usb_role_switch handle
> + * @role_sw_relay: usb_role_switch relay handle
>   * @role_switch_default_mode: default operation mode of controller while
>   *			usb role is USB_ROLE_NONE.
>   * @usb_psy: pointer to power supply interface.
> @@ -1136,6 +1137,7 @@ struct dwc3 {
>  	struct notifier_block	edev_nb;
>  	enum usb_phy_interface	hsphy_mode;
>  	struct usb_role_switch	*role_sw;
> +	struct usb_role_switch	*role_sw_relay;
>  	enum usb_dr_mode	role_switch_default_mode;
>  
>  	struct power_supply	*usb_psy;
> diff --git a/drivers/usb/dwc3/drd.c b/drivers/usb/dwc3/drd.c
> index 8fcbac10510c..74293861bd8f 100644
> --- a/drivers/usb/dwc3/drd.c
> +++ b/drivers/usb/dwc3/drd.c
> @@ -507,6 +507,9 @@ static int dwc3_usb_role_switch_set(struct usb_role_switch *sw,
>  	}
>  
>  	dwc3_set_mode(dwc, mode);
> +	if (dwc->role_sw_relay)
> +		usb_role_switch_set_role(dwc->role_sw_relay, role);
> +
>  	return 0;
>  }
>  
> @@ -563,6 +566,10 @@ static int dwc3_setup_role_switch(struct dwc3 *dwc)
>  	if (IS_ERR(dwc->role_sw))
>  		return PTR_ERR(dwc->role_sw);
>  
> +	dwc->role_sw_relay = usb_role_switch_get(dwc->dev);

So you're going to rely on DT to create a role-switch link between the
dwc3 core driver and the qcom wrapper?

As I said the other day, this is just a hack to get around the fact that
of_platform_populate() may return before the dwc3 core has probed.

Another such case can be seen in [1], where Wesley is patching the DT
node in runtime in order to pass a boolean parameter between the two
driver parts.

If we fix that we don't need these kinds of workarounds.

[1] https://lore.kernel.org/linux-arm-msm/1625218655-14180-6-git-send-email-wcheng@codeaurora.org/

Regards,
Bjorn

> +	if (IS_ERR(dwc->role_sw_relay))
> +		return PTR_ERR(dwc->role_sw_relay);
> +
>  	dwc3_set_mode(dwc, mode);
>  	return 0;
>  }
> @@ -630,6 +637,9 @@ void dwc3_drd_exit(struct dwc3 *dwc)
>  {
>  	unsigned long flags;
>  
> +	if (dwc->role_sw_relay)
> +		usb_role_switch_put(dwc->role_sw_relay);
> +
>  	if (dwc->role_sw)
>  		usb_role_switch_unregister(dwc->role_sw);
>  
> -- 
> 2.30.1
>