thermal/core: Add a check before calling set_trip_temp()

The thermal driver [0] for Renesas RZ/G2L SoC does not implement
set_trip_temp() callback but has trips commit 9326167058
("thermal/core: Move set_trip_temp ops to the sysfs code") changed
the behaviour which causes the below panic when trying to set the
trip temperature:

root@smarc-rzg2l:~# echo 51000 > /sys/class/thermal/thermal_zone0/trip_point_0_temp
[   92.461521] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[   92.470958] Mem abort info:
[   92.474311]   ESR = 0x0000000086000004
[   92.478546]   EC = 0x21: IABT (current EL), IL = 32 bits
[   92.484290]   SET = 0, FnV = 0
[   92.487693]   EA = 0, S1PTW = 0
[   92.491153]   FSC = 0x04: level 0 translation fault
[   92.496461] user pgtable: 4k pages, 48-bit VAs, pgdp=000000004e885000
[   92.503736] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
[   92.510869] Internal error: Oops: 86000004 [#3] PREEMPT SMP
[   92.516556] CPU: 0 PID: 290 Comm: sh Tainted: G      D            6.0.0-rc4-next-20220906-arm64-renesas-00124-g84633c87c5f6-dirty #509
[   92.528814] Hardware name: Renesas SMARC EVK based on r9a07g044l2 (DT)
[   92.535441] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   92.542516] pc : 0x0
[   92.544764] lr : trip_point_temp_store+0x84/0x140
[   92.549582] sp : ffff80000a92bc10
[   92.552961] x29: ffff80000a92bc10 x28: ffff00000d8a45c0 x27: 0000000000000000
[   92.560249] x26: 0000000000000000 x25: ffff8000082b53e8 x24: ffff00000eaffc20
[   92.567532] x23: ffff80000a92bd68 x22: ffff00000d3e0f80 x21: 0000000000000006
[   92.574814] x20: ffff800009149000 x19: ffff00000b8ab000 x18: 0000000000000000
[   92.582097] x17: 0000000000000000 x16: 0000000000000000 x15: 0000aaab028cdee0
[   92.589378] x14: 0000000000000000 x13: 0000000000000000 x12: ffff80000a92bbd0
[   92.596659] x11: ffff00000d3e0f80 x10: ffff800009149eb8 x9 : 000000000000000a
[   92.603940] x8 : 00000000ffffffc9 x7 : 0000000000000005 x6 : 000000000000002a
[   92.611220] x5 : 000000000000c738 x4 : 00000000ffffffd3 x3 : 0000000000000000
[   92.618500] x2 : 000000000000c738 x1 : 0000000000000000 x0 : ffff00000b8ab000
[   92.625781] Call trace:
[   92.628282]  0x0
[   92.630176]  dev_attr_store+0x14/0x28
[   92.633935]  sysfs_kf_write+0x4c/0x70
[   92.637681]  kernfs_fop_write_iter+0x160/0x1e0
[   92.642213]  vfs_write+0x474/0x540
[   92.645703]  ksys_write+0x68/0xf8
[   92.649100]  __arm64_sys_write+0x18/0x20
[   92.653111]  invoke_syscall+0x40/0xf8
[   92.656866]  el0_svc_common.constprop.3+0x88/0x110
[   92.661758]  do_el0_svc+0x20/0x78
[   92.665158]  el0_svc+0x3c/0x90
[   92.668291]  el0t_64_sync_handler+0x90/0xb8
[   92.672563]  el0t_64_sync+0x148/0x14c
[   92.676322] Code: bad PC value
[   92.679453] ---[ end trace 0000000000000000 ]---
/bin/start_getty: line 40:   290 Segmentation fault      ${setsid:-} ${getty} -L $1 $2 $3

Poky (Yocto Project Reference Distro) 3.2.1 smarc-rzg2l ttySC0

smarc-rzg2l login:

This patch fixes the above issue by adding a check to see if
set_trip_temp() callback is implemented before calling it.

[0] drivers/thermal/rzg2l_thermal.c

Fixes: 9326167058 ("thermal/core: Move set_trip_temp ops to the sysfs code")
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20220908174610.7837-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/thermal/thermal_sysfs.c

@@ -128,9 +128,11 @@ trip_point_temp_store(struct device *dev, struct device_attribute *attr,
 	if (kstrtoint(buf, 10, &temperature))
 		return -EINVAL;
 
-	ret = tz->ops->set_trip_temp(tz, trip, temperature);
-	if (ret)
-		return ret;
+	if (tz->ops->set_trip_temp) {
+		ret = tz->ops->set_trip_temp(tz, trip, temperature);
+		if (ret)
+			return ret;
+	}
 
 	if (tz->trips)
 		tz->trips[trip].temperature = temperature;