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

[Elson Serrao]

On 7/5/2026 11:46 PM, Peter Chen wrote:
> 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@xxxxxxxxxxxxxxxx>
>> ---
>>  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)
>


This could work, and we may be able to drop the additional flag.
The only behavioral difference I can see is that EUD would no
longer be re-enabled as part of exiting host mode. Instead, it
would remain disabled until an explicit switch to DEVICE role.

I think this should be fine, since EUD is only usable once a
cable is plugged in and we switch to DEVICE mode anyway. So the
user remains unaware that EUD is hardware-disabled until the
cable is plugged back in.

Let me try this out and make sure there aren't any other corner
cases.

Thanks,
Elson

 
> 
>>  	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
>>
>>
>