Since commit 262ca38f ("clk: Stop forwarding clk_rate_requests
to the parent"), the clk_rate_request is .. as the title says, not
forwarded anymore to the parent: this produces an issue with the
MediaTek clock MUX driver during GPU DVFS on MT8195, but not on
MT8192 or others.

This is because, differently from others, like MT8192 where all of
the clocks in the MFG parents tree are of mtk_mux type, but in the
parent tree of MT8195's MFG clock, we have one mtk_mux clock and
one (clk framework generic) mux clock, like so:

names: mfg_bg3d -> mfg_ck_fast_ref -> top_mfg_core_tmp (or) mfgpll
types: mtk_gate ->      mux        ->     mtk_mux      (or) mtk_pll

To solve this issue and also keep the GPU DVFS clocks code working
as expected, wire up a .determine_rate() callback for the mtk_mux
ops; for that, the standard clk_mux_determine_rate_flags() was used
as it was possible to.

This commit was successfully tested on MT6795 Xperia M5, MT8173 Elm,
MT8192 Spherion and MT8195 Tomato; no regressions were seen.

For the sake of some more documentation about this issue here's the
trace of it:

[   12.211587] ------------[ cut here ]------------
[   12.211589] WARNING: CPU: 6 PID: 78 at drivers/clk/clk.c:1462 clk_core_init_rate_req+0x84/0x90
[   12.211593] Modules linked in: stp crct10dif_ce mtk_adsp_common llc rfkill snd_sof_xtensa_dsp
               panfrost(+) sbs_battery cros_ec_lid_angle cros_ec_sensors snd_sof_of
               cros_ec_sensors_core hid_multitouch cros_usbpd_logger snd_sof gpu_sched
               snd_sof_utils fuse ipv6
[   12.211614] CPU: 6 PID: 78 Comm: kworker/u16:2 Tainted: G        W          6.0.0-next-20221011+ #58
[   12.211616] Hardware name: Acer Tomato (rev2) board (DT)
[   12.211617] Workqueue: devfreq_wq devfreq_monitor
[   12.211620] pstate: 40400009 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   12.211622] pc : clk_core_init_rate_req+0x84/0x90
[   12.211625] lr : clk_core_forward_rate_req+0xa4/0xe4
[   12.211627] sp : ffff80000893b8e0
[   12.211628] x29: ffff80000893b8e0 x28: ffffdddf92f9b000 x27: ffff46a2c0e8bc05
[   12.211632] x26: ffff46a2c1041200 x25: 0000000000000000 x24: 00000000173eed80
[   12.211636] x23: ffff80000893b9c0 x22: ffff80000893b940 x21: 0000000000000000
[   12.211641] x20: ffff46a2c1039f00 x19: ffff46a2c1039f00 x18: 0000000000000000
[   12.211645] x17: 0000000000000038 x16: 000000000000d904 x15: 0000000000000003
[   12.211649] x14: ffffdddf9357ce48 x13: ffffdddf935e71c8 x12: 000000000004803c
[   12.211653] x11: 00000000a867d7ad x10: 00000000a867d7ad x9 : ffffdddf90c28df4
[   12.211657] x8 : ffffdddf9357a980 x7 : 0000000000000000 x6 : 0000000000000004
[   12.211661] x5 : ffffffffffffffc8 x4 : 00000000173eed80 x3 : ffff80000893b940
[   12.211665] x2 : 00000000173eed80 x1 : ffff80000893b940 x0 : 0000000000000000
[   12.211669] Call trace:
[   12.211670]  clk_core_init_rate_req+0x84/0x90
[   12.211673]  clk_core_round_rate_nolock+0xe8/0x10c
[   12.211675]  clk_mux_determine_rate_flags+0x174/0x1f0
[   12.211677]  clk_mux_determine_rate+0x1c/0x30
[   12.211680]  clk_core_determine_round_nolock+0x74/0x130
[   12.211682]  clk_core_round_rate_nolock+0x58/0x10c
[   12.211684]  clk_core_round_rate_nolock+0xf4/0x10c
[   12.211686]  clk_core_set_rate_nolock+0x194/0x2ac
[   12.211688]  clk_set_rate+0x40/0x94
[   12.211691]  _opp_config_clk_single+0x38/0xa0
[   12.211693]  _set_opp+0x1b0/0x500
[   12.211695]  dev_pm_opp_set_rate+0x120/0x290
[   12.211697]  panfrost_devfreq_target+0x3c/0x50 [panfrost]
[   12.211705]  devfreq_set_target+0x8c/0x2d0
[   12.211707]  devfreq_update_target+0xcc/0xf4
[   12.211708]  devfreq_monitor+0x40/0x1d0
[   12.211710]  process_one_work+0x294/0x664
[   12.211712]  worker_thread+0x7c/0x45c
[   12.211713]  kthread+0x104/0x110
[   12.211716]  ret_from_fork+0x10/0x20
[   12.211718] irq event stamp: 7102
[   12.211719] hardirqs last  enabled at (7101): [<ffffdddf904ea5a0>] finish_task_switch.isra.0+0xec/0x2f0
[   12.211723] hardirqs last disabled at (7102): [<ffffdddf91794b74>] el1_dbg+0x24/0x90
[   12.211726] softirqs last  enabled at (6716): [<ffffdddf90410be4>] __do_softirq+0x414/0x588
[   12.211728] softirqs last disabled at (6507): [<ffffdddf904171d8>] ____do_softirq+0x18/0x24
[   12.211730] ---[ end trace 0000000000000000 ]---

Fixes: 262ca38f ("clk: Stop forwarding clk_rate_requests to the parent")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221011135548.318323-1-angelogioacchino.delregno@collabora.comSigned-off-by: Stephen Boyd <sboyd@kernel.org>