pmdomain: imx: gpcv2: Add delay after power up handshake

AudioMix BLK-CTRL on i.MX8MP encountered an accessing register issue
after power up.

[    2.181035] Kernel panic - not syncing: Asynchronous SError Interrupt
[    2.181038] CPU: 1 PID: 48 Comm: kworker/u16:2 Not tainted 6.9.0-rc5-next-20240424-00003-g21cec88845c6 torvalds#171
[    2.181047] Hardware name: NXP i.MX8MPlus EVK board (DT)
[    2.181050] Workqueue: events_unbound deferred_probe_work_func
[    2.181064] Call trace:
[...]
[    2.181142]  arm64_serror_panic+0x6c/0x78
[    2.181149]  do_serror+0x3c/0x70
[    2.181157]  el1h_64_error_handler+0x30/0x48
[    2.181164]  el1h_64_error+0x64/0x68
[    2.181171]  clk_imx8mp_audiomix_runtime_resume+0x34/0x44
[    2.181183]  __genpd_runtime_resume+0x30/0x80
[    2.181195]  genpd_runtime_resume+0x110/0x244
[    2.181205]  __rpm_callback+0x48/0x1d8
[    2.181213]  rpm_callback+0x68/0x74
[    2.181224]  rpm_resume+0x468/0x6c0
[    2.181234]  __pm_runtime_resume+0x50/0x94
[    2.181243]  pm_runtime_get_suppliers+0x60/0x8c
[    2.181258]  __driver_probe_device+0x48/0x12c
[    2.181268]  driver_probe_device+0xd8/0x15c
[    2.181278]  __device_attach_driver+0xb8/0x134
[    2.181290]  bus_for_each_drv+0x84/0xe0
[    2.181302]  __device_attach+0x9c/0x188
[    2.181312]  device_initial_probe+0x14/0x20
[    2.181323]  bus_probe_device+0xac/0xb0
[    2.181334]  deferred_probe_work_func+0x88/0xc0
[    2.181344]  process_one_work+0x150/0x290
[    2.181357]  worker_thread+0x2f8/0x408
[    2.181370]  kthread+0x110/0x114
[    2.181381]  ret_from_fork+0x10/0x20
[    2.181391] SMP: stopping secondary CPUs

According to comments in power up handshake:

	/* request the ADB400 to power up */
	if (domain->bits.hskreq) {
		regmap_update_bits(domain->regmap, domain->regs->hsk,
				   domain->bits.hskreq, domain->bits.hskreq);

		/*
		 * ret = regmap_read_poll_timeout(domain->regmap, domain->regs->hsk, reg_val,
		 *				  (reg_val & domain->bits.hskack), 0,
		 *				  USEC_PER_MSEC);
		 * Technically we need the commented code to wait handshake. But that needs
		 * the BLK-CTL module BUS clk-en bit being set.
		 *
		 * There is a separate BLK-CTL module and we will have such a driver for it,
		 * that driver will set the BUS clk-en bit and handshake will be triggered
		 * automatically there. Just add a delay and suppose the handshake finish
		 * after that.
		 */
	}

The BLK-CTL module needs to add delay to wait for a handshake request finished.
For some BLK-CTL module (eg. AudioMix on i.MX8MP) doesn't have BUS clk-en
bit, it is better to add delay in this driver, as the BLK-CTL module doesn't
need to care about how it is powered up.

regmap_read_bypassed() is to make sure the above write IO transaction already
reaches target before udelay().

Fixes: 1496dd4 ("clk: imx: imx8mp: Add pm_runtime support for power saving")
Reported-by: Francesco Dolcini <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Suggested-by: Frank Li <[email protected]>
Signed-off-by: Shengjiu Wang <[email protected]>
Tested-by: Adam Ford <[email protected]>
Tested-by: Alexander Stein <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Ulf Hansson <[email protected]>

drivers/pmdomain/imx/gpcv2.c

@@ -393,6 +393,17 @@ static int imx_pgc_power_up(struct generic_pm_domain *genpd)
 		 * automatically there. Just add a delay and suppose the handshake finish
 		 * after that.
 		 */
+
+		/*
+		 * For some BLK-CTL module (eg. AudioMix on i.MX8MP) doesn't have BUS
+		 * clk-en bit, it is better to add delay here, as the BLK-CTL module
+		 * doesn't need to care about how it is powered up.
+		 *
+		 * regmap_read_bypassed() is to make sure the above write IO transaction
+		 * already reaches target before udelay()
+		 */
+		regmap_read_bypassed(domain->regmap, domain->regs->hsk, &reg_val);
+		udelay(5);
 	}
 
 	/* Disable reset clocks for all devices in the domain */