Re: [PATCH] usb: usb251xb: check if hub is already attached

[Richard Leitner <richard.leitner@skidata.com>]

On Thu, Feb 27, 2020 at 09:14:48AM +0100, Uwe Kleine-König wrote:
> On Thu, Feb 27, 2020 at 08:25:45AM +0100, Marco Felsch wrote:
> > It is possible that the hub was configured earlier by the bootloader and
> > we lack of the reset-gpio. In such a case the usb251xb_connect() fails
> > because the registers are write-protected. Add a check to test if the
> > hub is already connected and don't try to reconfigure the hub if we
> > can't toggle the reset pin. Don't change the usb251xb_connect() logic
> > if we can't read the status.
> > 
> > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > ---
> >  drivers/usb/misc/usb251xb.c | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> > 
> > diff --git a/drivers/usb/misc/usb251xb.c b/drivers/usb/misc/usb251xb.c
> > index 29fe5771c21b..9f9a64bab059 100644
> > --- a/drivers/usb/misc/usb251xb.c
> > +++ b/drivers/usb/misc/usb251xb.c
> > @@ -266,6 +266,30 @@ static int usb251x_check_gpio_chip(struct usb251xb *hub)
> >  }
> >  #endif
> >  
> > +static bool usb251xb_hub_attached(struct usb251xb *hub)
> > +{
> > +	char i2c_rb;
> > +	int err;
> > +
> > +	err = i2c_smbus_read_block_data(hub->i2c, USB251XB_ADDR_STATUS_COMMAND,
> > +					&i2c_rb);
> > +	if (err < 0) {
> > +		/*
> > +		 * The device disables the i2c-interface immediately after it
> > +		 * received the USB_ATTACH signal.
> > +		 */
> > +		if (err == -ENXIO)
> > +			return true;
> > +
> > +		dev_warn(hub->dev,
> > +			 "Checking hub Status/Command register failed: %d\n",
> > +			 err);
> > +		return false;
> > +	}
> > +
> > +	return !!(i2c_rb & USB251XB_STATUS_COMMAND_ATTACH);
> > +}
> > +
> >  static void usb251xb_reset(struct usb251xb *hub)
> >  {
> >  	if (!hub->gpio_reset)
> > @@ -288,6 +312,15 @@ static int usb251xb_connect(struct usb251xb *hub)
> >  	struct device *dev = hub->dev;
> >  	int err, i;
> >  	char i2c_wb[USB251XB_I2C_REG_SZ];
> > +	bool is_attached;
> > +
> > +	/*
> > +	 * Check if configuration was done earlier by the bootloader. Trust them
> > +	 * if it is the case and we are not capable to reset the hub.
> > +	 */
> > +	is_attached = usb251xb_hub_attached(hub);
> > +	if (!hub->gpio_reset && is_attached)
> > +		return 0;
> 
> If you write this as:
> 
> 	if (!hub->gpio_reset && usb251xb_hub_attached(hub))
> 		return 0;
> 
> you save some i2c transfers in the presence of a reset gpio.

I'd also go with this solution, so you only have i2c transfers when a
reset gpio is configured/present.

> 
> Also I wonder if skipping the initialisation is at least worth a
> pr_info.

+1 for pr_info.

regards;rl

> 
> Best regards
> Uwe
> 
> -- 
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |