scsi: ufs: core: Hold a clock reference across the probe

Clock gating becomes possible as soon as ufshcd_init_clk_gating() has run,
and from that point on the probe keeps accessing host registers without
ever taking a clock reference. This has been safe only because of the state
check in __ufshcd_release(): gate_work is not queued unless
hba->ufshcd_state is UFSHCD_STATE_OPERATIONAL, and the promotion to that
state used to happen after the last register access of the probe, at the
end of ufshcd_probe_hba().

That is fragile: it only works while the promotion happens after the
register accesses. Commit a390e6677f41 ("scsi: ufs: core: Expand the
ufshcd_device_init(hba, true) call") changed that ordering by moving the
promotion into ufshcd_init(), which schedules ufshcd_async_scan()
afterwards. ufshcd_probe_hba() therefore now runs with the state already
promoted, and it accesses host registers without holding a clock reference:

 - On hosts with UFSHCD_QUIRK_REINIT_AFTER_MAX_GEAR_SWITCH it calls
   ufshcd_hba_stop() and ufshcd_hba_enable() before ufshcd_device_init()
   sets the state back to UFSHCD_STATE_RESET, and both read
   REG_CONTROLLER_ENABLE, so gated clocks stall there instead of just
   losing a write.

 - It ends with an ufshcd_configure_auto_hibern8() write, which its other
   callers do take a clock reference for.

Take a clock reference as soon as clock gating has been initialised and
keep it until the probe is over. It then does not matter who drops a clock
reference while the probe is running, and the register accesses of the
probe no longer depend on hba->ufshcd_state. The reference is dropped by
ufshcd_async_scan() once the scan has finished, or by the new out_release
label if the probe fails after it was taken.

Fixes: a390e6677f41 ("scsi: ufs: core: Expand the ufshcd_device_init(hba, true) call")
Signed-off-by: Naomi Chu <naomi.chu@mediatek.com>
Reviewed-by: Peter Wang <peter.wang@mediatek.com>
Link: https://patch.msgid.link/20260909091045.1134956-1-naomi.chu@mediatek.com
Signed-off-by: Martin K. Petersen (Oracle) <mkp@kernel.org>

0 files changed, 0 insertions, 0 deletions