i3c: dw: avoid shift-out-of-bounds when DAA assigns no devices

On an empty bus ENTDAA assigns nothing, so cmd->rx_len (the count
of addresses left unassigned) equals master->maxdevs.

The GENMASK() index master->maxdevs - cmd->rx_len - 1 then becomes -1,
which trips up UBSAN. This happens every time on boot on a Gigabyte/AMD
server:

    UBSAN: shift-out-of-bounds in drivers/i3c/master/dw-i3c-master.c:905:12
    shift exponent 64 is too large for 64-bit type 'long unsigned int'
    CPU: 7 UID: 0 PID: 963 Comm: (udev-worker) Not tainted 7.0.11-200.fc44.x86_64 #1 PREEMPT(lazy)
    Hardware name: Giga Computing E163-Z34-AAH1-000/MZ33-DC1-000, BIOS R32_F45 04/01/2026
    Call Trace:
     <TASK>
     dump_stack_lvl+0x5d/0x80
     ubsan_epilogue+0x5/0x2b
     __ubsan_handle_shift_out_of_bounds.cold+0xd7/0x1ab
     dw_i3c_master_daa.cold+0x1b/0x96 [dw_i3c_master]
     i3c_master_do_daa_ext.part.0+0x3e/0xf0 [i3c]

Skip the mask when no new device was assigned.

Fixes: 1dd728f5d4d4 ("i3c: master: Add driver for Synopsys DesignWare IP")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260630172904.2662160-1-kuba@kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

0 files changed, 0 insertions, 0 deletions