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

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Date:   Tue, 13 Nov 2018 17:41:09 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     stable@...r.kernel.org
CC:     Jerome Brunet <jbrunet@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>,
        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
Subject: Re: [PATCH v2] clk: meson-gxbb: set fclk_div3 as CLK_IS_CRITICAL

Le 13/11/2018 17:38, Neil Armstrong a écrit :
> Hi Stable team,
> 
> Le 06/11/2018 00:08, Jerome Brunet a écrit :
>> 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>
> 
> 
> Could this patch go into the next 4.18 stable release since it hit linus master with commit id e2576c8bdfd462c34b8a46c0084e7c30b0851bf4 ?

I forgot, but it should also go into the next 4.19 stable release aswell.

Neil

> Thanks,
> Neil
> 
>> ---
>>  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,
>>  	},
>>  };
>>  
>>