ichwd: Add manual for i6300esb watchdog

Reviewed by:    ziaee, mhorne
Approved by:    lwhsu (mentor)
MFC after:      2 weeks
Sponsored by:   The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D54466

share/man/man4/ichwd.4

@@ -23,7 +23,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd August 20, 2008
+.Dd January 3, 2026
 .Dt ICHWD 4
 .Os
 .Sh NAME
@@ -55,6 +55,16 @@ The ICH WDT counts down in ticks of approximately 0.6 seconds; the
 exact value depends on hardware quality and environmental factors.
 Supported watchdog intervals range from 2 to 63 ticks.
 .Pp
+In QEMU, there is a dedicated watchdog implementation for x86
+systems based on the Intel 6300ESB controller hub.
+Support for this watchdog is provided by this kernel module.
+.Pp
+Optionally, set the
+.Va hw.i6300esbwd.x.locked=1
+.Xr sysctl 8
+to prevent users from disabling the watchdog timeout check
+after it has been enabled.
+.Pp
 Note that on some ICH-based systems, the WDT may be present but
 disabled, either in hardware or by the BIOS.
 The