Re: git: ccabc7c2e556 - main - DEVICE_IDENTIFY.9: Modernize description and use cases

On Thu, Jan 09, 2025 at 08:20:55PM +0000, John Baldwin wrote:
> The branch main has been updated by jhb:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=ccabc7c2e556ac0b14da9b682b706ccaf251c0fe
> 
> commit ccabc7c2e556ac0b14da9b682b706ccaf251c0fe
> Author:     John Baldwin <jhb@FreeBSD.org>
> AuthorDate: 2025-01-09 20:20:16 +0000
> Commit:     John Baldwin <jhb@FreeBSD.org>
> CommitDate: 2025-01-09 20:20:16 +0000
> 
>     DEVICE_IDENTIFY.9: Modernize description and use cases
>     
>     Mention adding devices based on firmware tables and software-only
>     pseudo-devices as use cases for identify methods as those are more
>     common than reading random I/O ports to identify a legacy ISA device.
>     
>     Describe how device_find_chid can be used to avoid duplicates.  While
>     here, explicitly note that devices added in identify methods typically
>     use a fixed device name.
>     
>     Trim the cross-references a bit.
>     
>     Reviewed by:    ziaee, imp
>     Differential Revision:  https://reviews.freebsd.org/D48367
> ---
>  share/man/man9/DEVICE_IDENTIFY.9 | 52 +++++++++++++++++++---------------------
>  1 file changed, 25 insertions(+), 27 deletions(-)
> 
> diff --git a/share/man/man9/DEVICE_IDENTIFY.9 b/share/man/man9/DEVICE_IDENTIFY.9
> index d75c1a91ce4a..b10d94143050 100644
> --- a/share/man/man9/DEVICE_IDENTIFY.9
> +++ b/share/man/man9/DEVICE_IDENTIFY.9
> @@ -26,44 +26,46 @@
>  .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
>  .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>  .\"
> -.Dd January 15, 2017
> +.Dd January 9, 2025
>  .Dt DEVICE_IDENTIFY 9
>  .Os
>  .Sh NAME
>  .Nm DEVICE_IDENTIFY
> -.Nd identify a device, register it
> +.Nd identify new child devices and register them
>  .Sh SYNOPSIS
>  .In sys/param.h
>  .In sys/bus.h
>  .Ft void
>  .Fn DEVICE_IDENTIFY "driver_t *driver" "device_t parent"
So what is the 'parent' for driver which creates devices based on the
firmware tables?

>  .Sh DESCRIPTION
> -The identify function for a device is only needed for devices on buses
> -that cannot identify their children independently, e.g.\& the ISA bus.
> -It is used to recognize the device (usually done by accessing non-ambiguous
> -registers in the hardware) and to tell the kernel about it and thus
> -creating a new device instance.
> +The identify method of a device driver is used to add devices that cannot be
> +enumerated by the standard method on a bus device.
> +Devices can be enumerated in various ways including accessing non-ambiguous
> +device registers and parsing firmware tables.
> +Software-only pseudo devices are also often enumerated via identify methods.
>  .Pp
> +For each newly identified device,
> +a new device instance should be created by invoking the
>  .Xr BUS_ADD_CHILD 9
> -is used to register the device as a child of the bus.
> -The device's resources (such as IRQ and I/O ports) are registered
> -with the kernel by calling
> -.Fn bus_set_resource
> -for each resource (refer to
> +method.
> +If the identify method is able to discover other properties about the new
> +device, those should also be set.
> +For example, device resources should be added to the device by calling
>  .Xr bus_set_resource 9
> -for more information).
> +for each resource.
>  .Pp
> -Since the device tree and the device driver tree are disjoint, the
> -.Fn DEVICE_IDENTIFY
> -routine needs to take this into account.
> -If you load and unload your device driver that has the identify
> -routine, the child node has the potential for adding the same node
> -multiple times unless specific measure are taken to preclude that
> -possibility.
> +An identify method might be invoked multiple times.
> +If a device driver is unloaded and loaded,
> +the identify method will be called a second time after being reloaded.
> +As a result, the identify method should avoid duplicate devices.
> +Devices added by identify methods typically use a fixed device name
> +in which case
> +.Xr device_find_child 9
> +can be used to detect existing devices.
>  .Sh EXAMPLES
>  The following pseudo-code shows an example of a function that
>  probes for a piece of hardware and registers it and its resource
> -(an I/O port) with the kernel.
> +(an I/O port) with the parent bus device.
>  .Bd -literal
>  void
>  foo_identify(driver_t *driver, device_t parent)
> @@ -72,7 +74,7 @@ foo_identify(driver_t *driver, device_t parent)
>  
>  	retrieve_device_information;
>  	if (devices matches one of your supported devices &&
> -	    not already in device tree) {
> +	    device_get_child(parent, "foo", DEVICE_UNIT_ANY) == NULL) {
>  		child = BUS_ADD_CHILD(parent, 0, "foo", DEVICE_UNIT_ANY);
>  		bus_set_resource(child, SYS_RES_IOPORT, 0, FOO_IOADDR, 1);
>  	}
> @@ -82,11 +84,7 @@ foo_identify(driver_t *driver, device_t parent)
>  .Xr BUS_ADD_CHILD 9 ,
>  .Xr bus_set_resource 9 ,
>  .Xr device 9 ,
> -.Xr device_add_child 9 ,
> -.Xr DEVICE_ATTACH 9 ,
> -.Xr DEVICE_DETACH 9 ,
> -.Xr DEVICE_PROBE 9 ,
> -.Xr DEVICE_SHUTDOWN 9
> +.Xr device_find_child 9
>  .Sh AUTHORS
>  This manual page was written by
>  .An Alexander Langer Aq Mt alex@FreeBSD.org .