This has been enhanced. It should now be passed a pointer to the printer name in R4. This should be 20 characters or less in length (not including the terminator). Any character less than 32 is regarded as terminating the name.
Note that R4 is now preserved on return, and R0 is definitely corrupted (the PRM is silent on the fate of registers other than R1-R3 and R5-R7).
The printer name returned in R4 is always terminated by a zero (0) character regardless of what the terminating character was when the name was passed to PDriver_SetInfo.
If PDriver_SetInfo has not been called, then R4 will point to a zero length string on return from PDriver_Info.