On Thu, 3 May 2012, Dmitry Torokhov wrote: > On Thu, May 03, 2012 at 09:09:37AM -0700, Greg KH wrote: > > Hi Kay, > > > > I've been working on removing the old err() and dbg() functions in usb.h > > that have been there since the 2.2 kernel and replace them with calls to > > dev_err() and dev_dbg(), as that's what we want to have, especially with > > your dev_printk() reworks. > > > > In some recent changes in the input drivers, Dmitry noted that I was > > picking the "wrong" struct device to pass to these functions. I was > > using the "farthest down the tree" struct device that I could get to, in > > the USB input driver's case, the struct device for the input device, a > > "class" device. > > > > But that seems to produce an output that is less than helpful. Dmitry > > used this as an example output to show this for a serio device: > > dev_warn(&input_dev->dev, "warning using input device\n"); > > dev_warn(&serio->dev, "warning using parent serio device\n"); > > > > Produces: > > [ 1.903608] input input6: warning using input device > > [ 1.903612] psmouse serio1: warning using parent serio device > > > > Here it seems that the "one up from the lowest struct device" works > > best. > > > > So I tried this out with a usb to serial device, and got the following > > results. With the code: > > dev_err(&port->dev, "dev_err port->dev output\n"); > > dev_err(&serial->dev->dev, "dev_err serial->dev->dev output\n"); > > dev_err(&serial->interface->dev, "dev_err serial->interface->dev output\n"); > > dev_err(port->port.tty->dev, "dev_err port->port.tty->dev output\n"); > > > > I get: > > [ 68.519639] pl2303 ttyUSB0: dev_err port->dev output > > [ 68.519645] usb 2-1.2: dev_err serial->dev->dev output > > [ 68.519649] pl2303 2-1.2:1.0: dev_err serial->interface->dev output > > [ 68.519653] tty ttyUSB0: dev_err port->port.tty->dev output > > > > All of these "describe" the device being operated on in one fashion or > > the other, as they are struct devices that are easily accessable from > > the driver. > > > > My question is, what is the "best" thing to be doing here? > > > > I still think the "lowest" struct device would be best (in this case, > > the last line above from the port->port.tty->dev pointer), but what do > > you think is best for userspace to have here? > > My $.02: > > In general, drivers should emit messages for the devices they bind to. > This way driver like psmouse (which is serio subsystem driver) will emit > messages using serio port it is bound (or attempting to bind to): > > [ 1.903612] psmouse serio1: warning using parent serio device > > and drivers like wacom which bind to a USB interface will emit messages > using USB intraface, like: > > [ 1.234567] wacom 2-1.2:1.0: some error happened > > The benefit of using the device we are binding to is that it allows us > to crearly identify the driver that emits the error and we are using the > same device throughout (leaf device might not have been created yet and > we already need to emit an error or a warning). That's just what I was going to say. So for example, in the USB-serial example, the usb 2-1.2: dev_err serial->dev->dev output line isn't specific enough because it doesn't say which interface it applies to. The tty ttyUSB0: dev_err port->port.tty->dev output line is appropriate for a message emanating from the tty core, but not from a usb-serial driver. As for the other two: pl2303 ttyUSB0: dev_err port->dev output pl2303 2-1.2:1.0: dev_err serial->interface->dev output either one would be okay. You could choose between them depending on what part of the driver is involved. A part that handles the tty functions would use the first and a part that handles the USB communication would use the second. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
