linux-kernel - Re: [PATCH] clk: samsung: fsd: Mark PLL_CAM

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Message-ID: <1c6c56f7-bdda-4e14-9910-80e0cda0d631@kernel.org>
Date: Fri, 20 Sep 2024 14:36:37 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Inbaraj E <inbaraj.e@...sung.com>, 'Stephen Boyd' <sboyd@...nel.org>,
 alim.akhtar@...sung.com, cw00.choi@...sung.com, linux-clk@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
 mturquette@...libre.com, s.nawrocki@...sung.com
Cc: pankaj.dubey@...sung.com, gost.dev@...sung.com
Subject: Re: [PATCH] clk: samsung: fsd: Mark PLL_CAM_CSI as critical

On 20/09/2024 06:15, Inbaraj E wrote:
> 
> 
>> -----Original Message-----
>> From: Inbaraj E <inbaraj.e@...sung.com>
>> Sent: 20 September 2024 09:35
>> To: 'Krzysztof Kozlowski' <krzk@...nel.org>; 'Stephen Boyd'
>> <sboyd@...nel.org>; 'alim.akhtar@...sung.com'
>> <alim.akhtar@...sung.com>; 'cw00.choi@...sung.com'
>> <cw00.choi@...sung.com>; 'linux-clk@...r.kernel.org' <linux-
>> clk@...r.kernel.org>; 'linux-kernel@...r.kernel.org' <linux-
>> kernel@...r.kernel.org>; 'linux-samsung-soc@...r.kernel.org' <linux-
>> samsung-soc@...r.kernel.org>; 'mturquette@...libre.com'
>> <mturquette@...libre.com>; 's.nawrocki@...sung.com'
>> <s.nawrocki@...sung.com>
>> Cc: 'pankaj.dubey@...sung.com' <pankaj.dubey@...sung.com>;
>> 'gost.dev@...sung.com' <gost.dev@...sung.com>
>> Subject: RE: [PATCH] clk: samsung: fsd: Mark PLL_CAM_CSI as critical
>>
>>
>>
>>> -----Original Message-----
>>> From: Krzysztof Kozlowski <krzk@...nel.org>
>>> Sent: 19 September 2024 17:33
>>> To: Inbaraj E <inbaraj.e@...sung.com>; 'Stephen Boyd'
>>> <sboyd@...nel.org>; alim.akhtar@...sung.com;
>> cw00.choi@...sung.com;
>>> linux-clk@...r.kernel.org; linux-kernel@...r.kernel.org;
>>> linux-samsung- soc@...r.kernel.org; mturquette@...libre.com;
>>> s.nawrocki@...sung.com
>>> Cc: pankaj.dubey@...sung.com; gost.dev@...sung.com
>>> Subject: Re: [PATCH] clk: samsung: fsd: Mark PLL_CAM_CSI as critical
>>>
>>> On 19/09/2024 13:33, Inbaraj E wrote:
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: Stephen Boyd <sboyd@...nel.org>
>>>>> Sent: 19 September 2024 15:51
>>>>> To: Inbaraj E <inbaraj.e@...sung.com>; alim.akhtar@...sung.com;
>>>>> cw00.choi@...sung.com; krzk@...nel.org; linux-clk@...r.kernel.org;
>>>>> linux- kernel@...r.kernel.org; linux-samsung-soc@...r.kernel.org;
>>>>> mturquette@...libre.com; s.nawrocki@...sung.com
>>>>> Cc: pankaj.dubey@...sung.com; gost.dev@...sung.com; Inbaraj E
>>>>> <inbaraj.e@...sung.com>
>>>>> Subject: Re: [PATCH] clk: samsung: fsd: Mark PLL_CAM_CSI as
>>>>> critical
>>>>>
>>>>> Quoting Inbaraj E (2024-09-17 03:10:16)
>>>>>> PLL_CAM_CSI is the parent clock for the ACLK and PCLK in the
>>>>>> CMU_CAM_CSI block. When we gate ACLK or PCLK, the clock
>> framework
>>>>> will
>>>>>> subsequently disables the parent clocks(PLL_CAM_CSI). Disabling
>>>>>> PLL_CAM_CSI is causing sytem level halt.
>>>>>>
>>>>>> It was observed on FSD SoC, when we gate the ACLK and PCLK during
>>>>>> CSI stop streaming through pm_runtime_put system is getting halted.
>>>>>> So marking PLL_CAM_CSI as critical to prevent disabling.
>>>>>>
>>>>>> Signed-off-by: Inbaraj E <inbaraj.e@...sung.com>
>>>>>> ---
>>>>>
>>>>> Please add a fixes tag. Although this is likely a band-aid fix
>>>>> because marking something critical leaves it enabled forever.
>>>>
>>>> Sure, will add fixes tag. As per HW manual, this PLL_CAM_CSI is
>>>> supplying clock even for CMU SFR access of CSI block, so we can't
>>>> gate this.
>>>
>>> Hm, I am not so sure. The CMU driver should just take appropriate clock.
>>> Sprinkling CLK_CRITICAL looks as substitute of missing clock handling/
>>
>> As per HW design, PLL_CAM_CSI is responsible for suppling clock to CSI SFR,
>> CMU SFR and some internal block of CAM_CSI. In this some of the clock is not
>> handled by any driver but it is required for CSI to work properly. For example
>> CSI NOC clock. So this is the reason we are marking PLL_CAM_CSI as critical.
>>
> 
> This is clock hierarchy for CMU_CAM_CSI block.
> 
> PLL_CAM_CSI -----> DIVIDER --------> CSI_SFR clock
> 			|
> 			|----> DIVIDER --------> CMU_SFR clock
> 			|
> 			|----> DIVIDER --------> CSI NOC clock. 
> 

And what is the problem in adding proper handling in the driver? You
just described case valid for 99% of SoC components.

Best regards,
Krzysztof