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Wed, 12 Oct 2022 05:40:06 -0400 (EDT) Date: Wed, 12 Oct 2022 11:40:04 +0200 From: Maxime Ripard To: AngeloGioacchino Del Regno Cc: sboyd@kernel.org, mturquette@baylibre.com, matthias.bgg@gmail.com, chun-jie.chen@mediatek.com, miles.chen@mediatek.com, wenst@chromium.org, linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] clk: mediatek: clk-mux: Add .determine_rate() callback Message-ID: <20221012094004.jgiyvmbgomiyedik@houat> References: <20221011135548.318323-1-angelogioacchino.delregno@collabora.com> <20221012085555.3nls7ja56vlnaz2w@houat> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221012_024017_293694_97F7A8BD X-CRM114-Status: GOOD ( 39.31 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Oct 12, 2022 at 11:09:59AM +0200, AngeloGioacchino Del Regno wrote: > Il 12/10/22 10:55, Maxime Ripard ha scritto: > > Hi, > > > > On Tue, Oct 11, 2022 at 03:55:48PM +0200, AngeloGioacchino Del Regno wrote: > > > Since commit 262ca38f4b6e ("clk: Stop forwarding clk_rate_requests > > > to the parent"), the clk_rate_request is .. as the title says, not > > > forwarded anymore to the parent: > > > > It's not entirely true, the rate request should still be forwarded, but > > we don't pass the same instance of clk_rate_request anymore. > > > > > 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. > > > > It probably fixes things indeed, but I'm a bit worried that it just > > works around the actual issue instead of fixing the actual bug... > > > > > 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): [] finish_task_switch.isra.0+0xec/0x2f0 > > > [ 12.211723] hardirqs last disabled at (7102): [] el1_dbg+0x24/0x90 > > > [ 12.211726] softirqs last enabled at (6716): [] __do_softirq+0x414/0x588 > > > [ 12.211728] softirqs last disabled at (6507): [] ____do_softirq+0x18/0x24 > > > [ 12.211730] ---[ end trace 0000000000000000 ]--- > > > > ... Indeed, you shouldn't hit that warning at all. It happens in > > clk_core_round_rate_nolock, which takes (before your patch) the > > CLK_SET_RATE_PARENT branch. This indeed has been changed by the patch > > you mentioned, and will call clk_core_forward_rate_req() now, that in > > turn calls clk_core_init_rate_nolock(). > > > > I think the warning you hit is because core->parent is NULL, which is > > passed to clk_core_forward_rate_req() as the parent argument, and we'll > > call clk_core_init_rate_req() with parent set as the core argument. > > > > In clk_core_init_rate_req(), the first thing we do is a WARN_ON(!core), > > which is what you hit here I think. > > > > This is different to the previous behavior that was calling > > clk_core_round_rate_nolock() with core->parent directly, and > > clk_core_round_rate_nolock() if its core argument is NULL will set > > req->rate to 0 and bail out without returning an error. > > > > Now, your patch probably works because now that you provide a > > determine_rate implementation, clk_core_can_round() returns true and > > you'll take a different branch in clk_core_round_rate_nolock(), avoiding > > that issue entirely. > > > > Does that patch work better (on top of next-20221012)? > > I admit I didn't go too deep in the research, as my brain processed that as > "this is a mux clock, not really different from a standard mux, this callback > is missing, that's not optimal"... then that fixed it and called it a day. > > I should've prolonged my research for a better understanding of what was > actually going on. No worries :) > What you said actually opened my mind and, with little surprise, your patch > works as good as mine - no warnings and the clock scales as expected! I'm actually wondering if you didn't encounter two issues. What kernel were you testing before? If it's older than today's next (next-20221012), you're likely missing https://lore.kernel.org/linux-clk/20221010-rpi-clk-fixes-again-v1-0-d87ba82ac404@cerno.tech/ Which is likely to be what fixed the clock scaling. And my patch only fixed the warning. Could you test next-20221012? If I'm right, you should only get the warning. > I still think that the mtk-mux driver should get a determine_rate callback but, > at this point, that's going to have an entirely different commit description... Yeah, it might, but as you said it's a separate discussion > Please go on and send your patch: if you want, please remember to add me to > the Cc's, so that I can give you my R-b tag in a timely manner. Thanks! Maxime _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel