Re: [PATCH v4 1/2] usb: misc: onboard_usb_hub: Add reset-gpio support

[Matthias Kaehlcke <mka@chromium.org>]

Hi Alexander,

(copying my comments from v3 to keep the discussion on the latest version)

On Wed, Jul 27, 2022 at 04:11:16PM +0200, Alexander Stein wrote:
> Despite default reset upon probe, release reset line after powering up
> the hub and assert reset again before powering down.
> 
> Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> ---
> * Patch 1 dropped as it already applied
> 
> Changes in v4:
> * Rebased to [1] commit e0c6b1f3d757 ("USB: usbsevseg: convert sysfs snprintf to sysfs_emit")
> * Added platform data for usb424
>   Reset pulse length taken from [2], Table 3-2 Symbol RESET_N
>   Completely untested
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git Branch usb-testing
> [2] http://ww1.microchip.com/downloads/en/devicedoc/00001692c.pdf
> 
>  drivers/usb/misc/onboard_usb_hub.c | 28 ++++++++++++++++++++++++++++
>  drivers/usb/misc/onboard_usb_hub.h | 22 +++++++++++++++++-----
>  2 files changed, 45 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/misc/onboard_usb_hub.c b/drivers/usb/misc/onboard_usb_hub.c
> index de3627af3c84..0c81417dd9a7 100644
> --- a/drivers/usb/misc/onboard_usb_hub.c
> +++ b/drivers/usb/misc/onboard_usb_hub.c
> @@ -7,6 +7,7 @@
>  
>  #include <linux/device.h>
>  #include <linux/export.h>
> +#include <linux/gpio/consumer.h>
>  #include <linux/init.h>
>  #include <linux/kernel.h>
>  #include <linux/list.h>
> @@ -38,6 +39,8 @@ struct usbdev_node {
>  struct onboard_hub {
>  	struct regulator *vdd;
>  	struct device *dev;
> +	const struct onboard_hub_pdata *pdata;
> +	struct gpio_desc *reset_gpio;
>  	bool always_powered_in_suspend;
>  	bool is_powered_on;
>  	bool going_away;
> @@ -56,6 +59,9 @@ static int onboard_hub_power_on(struct onboard_hub *hub)
>  		return err;
>  	}
>  
> +	fsleep(hub->pdata->reset_us);
> +	gpiod_set_value_cansleep(hub->reset_gpio, 0);
> +
>  	hub->is_powered_on = true;
>  
>  	return 0;
> @@ -65,6 +71,11 @@ static int onboard_hub_power_off(struct onboard_hub *hub)
>  {
>  	int err;
>  
> +	if (hub->reset_gpio) {
> +		gpiod_set_value_cansleep(hub->reset_gpio, 1);
> +		fsleep(hub->pdata->reset_us);

Is this delay here actually needed? There is a delay in onboard_hub_power_on(),
before de-asserting the reset, isn't that enough?

> +	}
> +
>  	err = regulator_disable(hub->vdd);
>  	if (err) {
>  		dev_err(hub->dev, "failed to disable regulator: %d\n", err);
> @@ -219,6 +230,7 @@ static void onboard_hub_attach_usb_driver(struct work_struct *work)
>  
>  static int onboard_hub_probe(struct platform_device *pdev)
>  {
> +	const struct of_device_id *of_id;
>  	struct device *dev = &pdev->dev;
>  	struct onboard_hub *hub;
>  	int err;
> @@ -227,10 +239,26 @@ static int onboard_hub_probe(struct platform_device *pdev)
>  	if (!hub)
>  		return -ENOMEM;
>  
> +	of_id = of_match_device(onboard_hub_match, &pdev->dev);
> +	if (!of_id)
> +		return -ENODEV;
> +
> +	hub->pdata = of_id->data;
> +	if (!hub->pdata)
> +		return -EINVAL;
> +
>  	hub->vdd = devm_regulator_get(dev, "vdd");
>  	if (IS_ERR(hub->vdd))
>  		return PTR_ERR(hub->vdd);
>  
> +	hub->reset_gpio = devm_gpiod_get_optional(dev, "reset",
> +						  GPIOD_OUT_HIGH);
> +	if (IS_ERR(hub->reset_gpio))
> +		return dev_err_probe(dev, PTR_ERR(hub->reset_gpio), "failed to get reset GPIO\n");
> +
> +	if (hub->reset_gpio)
> +		fsleep(hub->pdata->reset_us);

Same question here: onboard_hub_power_on() is called a few lines below and
has a delay before de-asserting the reset. Is the delay here really needed?