Re: [PATCH V6 09/21] clk: tegra: clk-super: Fix to enable PLLP branches to CPU

From: Sowjanya Komatineni <skomatineni@nvidia.com>
To: Dmitry Osipenko <digetx@gmail.com>, <thierry.reding@gmail.com>,
	<jonathanh@nvidia.com>, <tglx@linutronix.de>,
	<jason@lakedaemon.net>, <marc.zyngier@arm.com>,
	<linus.walleij@linaro.org>, <stefan@agner.ch>,
	<mark.rutland@arm.com>
Cc: <pdeschrijver@nvidia.com>, <pgaikwad@nvidia.com>,
	<sboyd@kernel.org>, <linux-clk@vger.kernel.org>,
	<linux-gpio@vger.kernel.org>, <jckuo@nvidia.com>,
	<josephl@nvidia.com>, <talho@nvidia.com>,
	<linux-tegra@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<mperttunen@nvidia.com>, <spatra@nvidia.com>,
	<robh+dt@kernel.org>, <devicetree@vger.kernel.org>
Subject: Re: [PATCH V6 09/21] clk: tegra: clk-super: Fix to enable PLLP branches to CPU
Date: Mon, 22 Jul 2019 00:24:13 -0700	[thread overview]
Message-ID: <90e1a90b-1d33-a5db-9af8-dc5c5d45b65f@nvidia.com> (raw)
In-Reply-To: <07897688-2a02-b7a7-7048-72c4078d26a2@gmail.com>

On 7/22/19 12:17 AM, Dmitry Osipenko wrote:
> 22.07.2019 10:12, Sowjanya Komatineni пишет:
>> On 7/21/19 11:32 PM, Dmitry Osipenko wrote:
>>> 22.07.2019 6:17, Sowjanya Komatineni пишет:
>>>> On 7/21/19 3:39 PM, Sowjanya Komatineni wrote:
>>>>> On 7/21/19 2:16 PM, Dmitry Osipenko wrote:
>>>>>> 21.07.2019 22:40, Sowjanya Komatineni пишет:
>>>>>>> This patch has a fix to enable PLLP branches to CPU before changing
>>>>>>> the CPU clusters clock source to PLLP for Gen5 Super clock.
>>>>>>>
>>>>>>> During system suspend entry and exit, CPU source will be switched
>>>>>>> to PLLP and this needs PLLP branches to be enabled to CPU prior to
>>>>>>> the switch.
>>>>>>>
>>>>>>> On system resume, warmboot code enables PLLP branches to CPU and
>>>>>>> powers up the CPU with PLLP clock source.
>>>>>>>
>>>>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
>>>>>>> ---
>>>>>>>     drivers/clk/tegra/clk-super.c            | 11 +++++++++++
>>>>>>>     drivers/clk/tegra/clk-tegra-super-gen4.c |  4 ++--
>>>>>>>     drivers/clk/tegra/clk.h                  |  4 ++++
>>>>>>>     3 files changed, 17 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/clk/tegra/clk-super.c
>>>>>>> b/drivers/clk/tegra/clk-super.c
>>>>>>> index 39ef31b46df5..d73c587e4853 100644
>>>>>>> --- a/drivers/clk/tegra/clk-super.c
>>>>>>> +++ b/drivers/clk/tegra/clk-super.c
>>>>>>> @@ -28,6 +28,9 @@
>>>>>>>     #define super_state_to_src_shift(m, s) ((m->width * s))
>>>>>>>     #define super_state_to_src_mask(m) (((1 << m->width) - 1))
>>>>>>>     +#define CCLK_SRC_PLLP_OUT0 4
>>>>>>> +#define CCLK_SRC_PLLP_OUT4 5
>>>>>>> +
>>>>>>>     static u8 clk_super_get_parent(struct clk_hw *hw)
>>>>>>>     {
>>>>>>>         struct tegra_clk_super_mux *mux = to_clk_super_mux(hw);
>>>>>>> @@ -97,6 +100,14 @@ static int clk_super_set_parent(struct clk_hw
>>>>>>> *hw, u8 index)
>>>>>>>             if (index == mux->div2_index)
>>>>>>>                 index = mux->pllx_index;
>>>>>>>         }
>>>>>>> +
>>>>>>> +    /*
>>>>>>> +     * Enable PLLP branches to CPU before selecting PLLP source
>>>>>>> +     */
>>>>>>> +    if ((mux->flags & TEGRA_CPU_CLK) &&
>>>>>>> +        ((index == CCLK_SRC_PLLP_OUT0) || (index ==
>>>>>>> CCLK_SRC_PLLP_OUT4)))
>>>>>>> +        tegra_clk_set_pllp_out_cpu(true);
>>>>>> Should somewhere here be tegra_clk_set_pllp_out_cpu(false) when
>>>>>> switching from PLLP?
>>>>> PLLP may be used for other CPU clusters.
>>>> Though to avoid flag and check needed to make sure other CPU is not
>>>> using before disabling PLLP branch to CPU.
>>>>
>>>> But leaving it enabled shouldn't impact much as clock source mux is
>>>> after this in design anyway.
>>>>
>>>> But can add as well if its clear that way.
>>> The TRM doc says "The CPU subsystem supports a switch-cluster mode
>>> meaning that only one of the clusters can be active at any given time".
>>>
>>> Given that cluster-switching isn't supported in upstream, I don't think
>>> that you need to care about the other cluster at all, at least for now.
>>>
>>> The cluster-switching implementation in upstream is very complicated
>>> because it requires a special "hotplugging" CPU governor, which
>>> apparently no other platform needs.
>>>
>>> [snip]
>> This patch enables PLLP branches to CPU for both CPUG & CPULP if they
>> use PLLP source.
>>
>> So, to disable PLLP out CPU when not in use, we still need check for
>> other cluster because during resume both LP CPU and G CPU gets restored.
>> CPUG runs from PLLP on resume and when it does super clk restore for LP
>> CPU which may not be using PLLP, but as both uses same super mux
>> clk_ops, without check (for PLLP branch to CPU in use) disabling PLLP
>> branch to CPU during LP CPU restore looses clock to CPU G as well which
>> is running from PLLP.
>>
>> Will add check and disable PLLP if not in use in next version... this
>> need extern flag as well to mark PLLP usage with either of CPU's.
> I still don't understand why do you need to care about LP cluster at
> all, given that it's always in a power-gated state.

cclk_lp is registered thru super clk mux which uses same clk_ops as cclk_g.

during restore, cclk_lp also gets restored. So both cclk_lp & cclk_g 
goes thru same clk_ops

In this patch, I marked super flags with TEGRA_CPU_CLK for both cclk_lp 
& cclk_g.

So when cclk_lp restore happens, it goes thru same set_parent clk_ops 
and as its source is not PLLP, it tries to disable PLLP_OUT_CPU if its 
disabled without adding check for PLLP being in use by other cluster.

So either I should not mark cclk_lp as TEGRA_CPU_CLK and mark cclk_g 
only as TEGRA_CPU_CLK so PLLP out to CPU can be disabled without check 
if its not the source.

OR

With TEGRA_CPU_CLK used for both cclk_lp & cclk_g, need to add check if 
PLLP is in use so during cclk_lp restore it doesnt disable PLLP out to CPU.

To simplify without check, will just mark cclk_g super clock flag only 
as TEGRA_CPU_CLK so PLLP_OUT_CPU enable or disable happens only for CPUG