Re: [PATCH v4 6/9] usb: misc: qcom_eud: add host mode coordination

[Peter Chen <peter.chen@kernel.org>]

On 26-05-01 10:06:32, Elson Serrao wrote:
> EUD functions by presenting itself as a USB device to the host PC for
> debugging, making it incompatible with USB host mode configurations.
> Enabling EUD while in host mode can also cause the USB controller to
> misbehave, as the EUD hub supports only a single upstream-facing port.
> 
> Handle the following scenarios to prevent these conflicts:
> 1. Prevent the user from enabling EUD via sysfs when the USB port is in
>    host mode.
> 2. Automatically disable EUD when the USB port switches to host mode,
>    and re-enable it when exiting host mode.
> 
> This ensures consistent state management without creating conflicts
> between the EUD debug hub and the USB controller.
> 
> Signed-off-by: Elson Serrao <elson.serrao@oss.qualcomm.com>
> ---
>  drivers/usb/misc/qcom_eud.c | 65 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 64 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/misc/qcom_eud.c b/drivers/usb/misc/qcom_eud.c
> index f656ffc8818a..4734b6307a85 100644
> --- a/drivers/usb/misc/qcom_eud.c
> +++ b/drivers/usb/misc/qcom_eud.c
> @@ -55,12 +55,15 @@ struct eud_chip {
>  	struct device			*dev;
>  	void __iomem			*base;
>  	struct eud_path			*paths[EUD_MAX_PORTS];
> +	/* serializes EUD control operations */
> +	struct mutex			state_lock;
>  	phys_addr_t			mode_mgr;
>  	unsigned int			int_status;
>  	int				irq;
>  	bool				enabled;
>  	bool				usb_attached;
>  	bool				phy_enabled;
> +	bool				eud_disabled_for_host;

Could just use below two conditions for EUD enable/disable judgement:

Enable:
(path->curr_role == USB_ROLE_DEVICE) && (chip->enabled == true)

Disable:
(path->curr_role != USB_ROLE_DEVICE) || (chip->enabled == false)

Peter

>  	u8				port_idx;
>  };
>  
> @@ -156,17 +159,43 @@ static ssize_t enable_store(struct device *dev,
>  		const char *buf, size_t count)
>  {
>  	struct eud_chip *chip = dev_get_drvdata(dev);
> +	struct eud_path *path;
>  	bool enable;
>  	int ret;
>  
>  	if (kstrtobool(buf, &enable))
>  		return -EINVAL;
>  
> +	guard(mutex)(&chip->state_lock);
> +
>  	/* Skip operation if already in desired state */
>  	if (chip->enabled == enable)
>  		return count;
>  
> +	/*
> +	 * Handle double-disable scenario: User is disabling EUD that was already
> +	 * disabled due to host mode. Since the hardware is already disabled, we
> +	 * only need to clear the host-disabled flag to prevent unwanted re-enabling
> +	 * when exiting host mode. This respects the user's explicit disable request.
> +	 */
> +	if (!enable && chip->eud_disabled_for_host) {
> +		chip->eud_disabled_for_host = false;
> +		chip->enabled = false;
> +		return count;
> +	}
> +
>  	if (enable) {
> +		/*
> +		 * EUD functions by presenting itself as a USB device to the host PC for
> +		 * debugging, making it incompatible with USB host mode configuration.
> +		 * Prevent enabling EUD in this configuration to avoid hardware conflicts.
> +		 */
> +		path = chip->paths[chip->port_idx];
> +		if (path->curr_role == USB_ROLE_HOST) {
> +			dev_err(chip->dev, "cannot enable EUD: USB port is in host mode\n");
> +			return -EBUSY;
> +		}
> +
>  		ret = enable_eud(chip);
>  		if (ret) {
>  			dev_err(chip->dev, "failed to enable eud\n");
> @@ -308,9 +337,41 @@ static irqreturn_t handle_eud_irq_thread(int irq, void *data)
>  static int eud_role_switch_set(struct usb_role_switch *sw, enum usb_role role)
>  {
>  	struct eud_path *path = usb_role_switch_get_drvdata(sw);
> +	struct eud_chip *chip = path->chip;
>  	int ret;
>  
> -	/* Forward the role request to the USB controller */
> +	guard(mutex)(&chip->state_lock);
> +
> +	/*
> +	 * EUD must be disabled when USB operates in host mode. EUD functions by
> +	 * presenting itself as a USB device to the host PC for debugging, making
> +	 * it incompatible with host mode configuration.
> +	 *
> +	 * chip->enabled preserves user's sysfs configuration and is not modified
> +	 * during host mode transitions to maintain user intent.
> +	 */
> +
> +	/* Only act if EUD is enabled and this is the active path */
> +	if (chip->enabled && path->num == chip->port_idx) {
> +		if (role == USB_ROLE_HOST && !chip->eud_disabled_for_host) {
> +			ret = disable_eud(chip);
> +			if (ret) {
> +				dev_err(chip->dev, "failed to disable EUD for host mode: %d\n",
> +					ret);
> +				return ret;
> +			}
> +			chip->eud_disabled_for_host = true;
> +		} else if (role != USB_ROLE_HOST && chip->eud_disabled_for_host) {
> +			ret = enable_eud(chip);
> +			if (ret) {
> +				dev_err(chip->dev, "failed to re-enable EUD after host mode: %d\n",
> +					ret);
> +				return ret;
> +			}
> +			chip->eud_disabled_for_host = false;
> +		}
> +	}
> +
>  	ret = usb_role_switch_set_role(path->controller_sw, role);
>  	if (ret) {
>  		dev_err(path->chip->dev, "failed to set role %s for port %u: %d\n",
> @@ -424,6 +485,8 @@ static int eud_probe(struct platform_device *pdev)
>  
>  	chip->dev = &pdev->dev;
>  
> +	mutex_init(&chip->state_lock);
> +
>  	for_each_child_of_node_scoped(np, child) {
>  		ret = eud_init_path(chip, child);
>  		if (ret)
> -- 
> 2.34.1
> 
> 

-- 

Thanks,
Peter Chen