Re: [PATCH v5 6/9] usb: misc: qcom_eud: add role-based EUD control

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

On 26-08-02 20:15:31, Elson Serrao wrote:
> EUD functions by presenting itself as a USB device to the host PC and is
> therefore only applicable when the port operates in device role. Keeping
> EUD enabled in other roles provides no benefit and unnecessarily keeps
> the associated PHY resources enabled. Furthermore, enabling EUD in host
> role can cause the USB controller to misbehave because the EUD hub
> supports only a single upstream-facing port.
> 
> Address this by treating EUD as usable only in device role. The
> role-switch callback enables or disables EUD as the port enters or
> leaves device role. A sysfs enable request made outside device role is
> recorded and honored when the port subsequently switches to device role.
> 
> Signed-off-by: Elson Serrao <elson.serrao@oss.qualcomm.com>

Reviewed-by: Peter Chen <peter.chen@kernel.org>

Peter
> ---
>  drivers/usb/misc/qcom_eud.c | 46 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/misc/qcom_eud.c b/drivers/usb/misc/qcom_eud.c
> index e83a4402e4b8..538e070cc140 100644
> --- a/drivers/usb/misc/qcom_eud.c
> +++ b/drivers/usb/misc/qcom_eud.c
> @@ -15,6 +15,7 @@
>  #include <linux/phy/phy.h>
>  #include <linux/platform_device.h>
>  #include <linux/slab.h>
> +#include <linux/string_choices.h>
>  #include <linux/sysfs.h>
>  #include <linux/usb/role.h>
>  #include <linux/firmware/qcom/qcom_scm.h>
> @@ -55,6 +56,8 @@ 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;
> @@ -156,17 +159,33 @@ 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;
>  
>  	if (enable) {
> +		path = chip->paths[chip->port_idx];
> +
> +		/*
> +		 * If not yet in device role, honor the userspace request and defer
> +		 * EUD enablement until the port transitions to device role in the
> +		 * set_role callback.
> +		 */
> +		if (path->curr_role != USB_ROLE_DEVICE) {
> +			dev_info(chip->dev, "Deferring EUD enable until port enters device mode\n");
> +			chip->enabled = enable;
> +			return count;
> +		}
> +
>  		ret = enable_eud(chip);
>  		if (ret) {
>  			dev_err(chip->dev, "failed to enable eud\n");
> @@ -304,7 +323,30 @@ 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);
> -	int ret;
> +	struct eud_chip *chip = path->chip;
> +	int ret = 0;
> +
> +	guard(mutex)(&chip->state_lock);
> +
> +	/*
> +	 * EUD is usable only in device role. Power it down for every other
> +	 * role to avoid keeping an unusable module 'ON'. chip->enabled
> +	 * preserves user's sysfs configuration and is not modified across
> +	 * role transitions.
> +	 */
> +	if (chip->enabled && path->num == chip->port_idx && role != path->curr_role) {
> +		if (role == USB_ROLE_DEVICE)
> +			ret = enable_eud(chip);
> +		else if (path->curr_role == USB_ROLE_DEVICE)
> +			ret = disable_eud(chip);
> +
> +		if (ret) {
> +			dev_err(chip->dev, "failed to %s EUD for role %s: %d\n",
> +				str_enable_disable(role == USB_ROLE_DEVICE),
> +				usb_role_string(role), ret);
> +			return ret;
> +		}
> +	}
>  
>  	/* Forward the role request to the USB controller */
>  	ret = usb_role_switch_set_role(path->controller_sw, role);
> @@ -431,6 +473,8 @@ 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