linux-kernel - [PATCH v2] clk: meson-gxbb: set fclk_div3 as CLK_IS

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Message-Id: <20181105230820.3562-1-jbrunet@baylibre.com>
Date:   Tue,  6 Nov 2018 00:08:20 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Neil Armstrong <narmstrong@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>
Cc:     Christian Hewitt <christianshewitt@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jerome Brunet <jbrunet@...libre.com>
Subject: [PATCH v2] clk: meson-gxbb: set fclk_div3 as CLK_IS_CRITICAL

From: Christian Hewitt <christianshewitt@...il.com>

On the Khadas VIM2 (GXM) and LePotato (GXL) board there are problems
with reboot; e.g. a ~60 second delay between issuing reboot and the
board power cycling (and in some OS configurations reboot will fail
and require manual power cycling).

Similar to 'commit c987ac6f1f088663b6dad39281071aeb31d450a8 ("clk:
meson-gxbb: set fclk_div2 as CLK_IS_CRITICAL")' the SCPI Cortex-M4
Co-Processor seems to depend on FCLK_DIV3 being operational.

Until commit 05f814402d6174369b3b29832cbb5eb5ed287059 ("clk:
meson: add fdiv clock gates"), this clock was modeled and left on by
the bootloader.

We don't have precise documentation about the SCPI Co-Processor and
its clock requirement so we are learning things the hard way.

Marking this clock as critical solves the problem but it should not
be viewed as final solution. Ideally, the SCPI driver should claim
these clocks. We also depends on some clock hand-off mechanism
making its way to CCF, to make sure the clock stays on between its
registration and the SCPI driver probe.

Fixes: 05f814402d61 ("clk: meson: add fdiv clock gates")
Signed-off-by: Christian Hewitt <christianshewitt@...il.com>
Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
---
 drivers/clk/meson/gxbb.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/clk/meson/gxbb.c b/drivers/clk/meson/gxbb.c
index 9309cfaaa464..4ada9668fd49 100644
--- a/drivers/clk/meson/gxbb.c
+++ b/drivers/clk/meson/gxbb.c
@@ -506,6 +506,18 @@ static struct clk_regmap gxbb_fclk_div3 = {
 		.ops = &clk_regmap_gate_ops,
 		.parent_names = (const char *[]){ "fclk_div3_div" },
 		.num_parents = 1,
+		/*
+		 * FIXME:
+		 * This clock, as fdiv2, is used by the SCPI FW and is required
+		 * by the platform to operate correctly.
+		 * Until the following condition are met, we need this clock to
+		 * be marked as critical:
+		 * a) The SCPI generic driver claims and enable all the clocks
+		 *    it needs
+		 * b) CCF has a clock hand-off mechanism to make the sure the
+		 *    clock stays on until the proper driver comes along
+		 */
+		.flags = CLK_IS_CRITICAL,
 	},
 };

-- 
2.19.1