RE: [PATCH] clk: samsung: fsd: Mark PLL_CAM_CSI as critical

["Inbaraj E" <inbaraj.e@xxxxxxxxxxx>]

> -----Original Message-----
> From: Inbaraj E <inbaraj.e@xxxxxxxxxxx>
> Sent: 20 September 2024 09:35
> To: 'Krzysztof Kozlowski' <krzk@xxxxxxxxxx>; 'Stephen Boyd'
> <sboyd@xxxxxxxxxx>; 'alim.akhtar@xxxxxxxxxxx'
> <alim.akhtar@xxxxxxxxxxx>; 'cw00.choi@xxxxxxxxxxx'
> <cw00.choi@xxxxxxxxxxx>; 'linux-clk@xxxxxxxxxxxxxxx' <linux-
> clk@xxxxxxxxxxxxxxx>; 'linux-kernel@xxxxxxxxxxxxxxx' <linux-
> kernel@xxxxxxxxxxxxxxx>; 'linux-samsung-soc@xxxxxxxxxxxxxxx' <linux-
> samsung-soc@xxxxxxxxxxxxxxx>; 'mturquette@xxxxxxxxxxxx'
> <mturquette@xxxxxxxxxxxx>; 's.nawrocki@xxxxxxxxxxx'
> <s.nawrocki@xxxxxxxxxxx>
> Cc: 'pankaj.dubey@xxxxxxxxxxx' <pankaj.dubey@xxxxxxxxxxx>;
> 'gost.dev@xxxxxxxxxxx' <gost.dev@xxxxxxxxxxx>
> Subject: RE: [PATCH] clk: samsung: fsd: Mark PLL_CAM_CSI as critical
> 
> 
> 
> > -----Original Message-----
> > From: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
> > Sent: 19 September 2024 17:33
> > To: Inbaraj E <inbaraj.e@xxxxxxxxxxx>; 'Stephen Boyd'
> > <sboyd@xxxxxxxxxx>; alim.akhtar@xxxxxxxxxxx;
> cw00.choi@xxxxxxxxxxx;
> > linux-clk@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > linux-samsung- soc@xxxxxxxxxxxxxxx; mturquette@xxxxxxxxxxxx;
> > s.nawrocki@xxxxxxxxxxx
> > Cc: pankaj.dubey@xxxxxxxxxxx; gost.dev@xxxxxxxxxxx
> > 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@xxxxxxxxxx>
> > >> Sent: 19 September 2024 15:51
> > >> To: Inbaraj E <inbaraj.e@xxxxxxxxxxx>; alim.akhtar@xxxxxxxxxxx;
> > >> cw00.choi@xxxxxxxxxxx; krzk@xxxxxxxxxx; linux-clk@xxxxxxxxxxxxxxx;
> > >> linux- kernel@xxxxxxxxxxxxxxx; linux-samsung-soc@xxxxxxxxxxxxxxx;
> > >> mturquette@xxxxxxxxxxxx; s.nawrocki@xxxxxxxxxxx
> > >> Cc: pankaj.dubey@xxxxxxxxxxx; gost.dev@xxxxxxxxxxx; Inbaraj E
> > >> <inbaraj.e@xxxxxxxxxxx>
> > >> 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@xxxxxxxxxxx>
> > >>> ---
> > >>
> > >> 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. 

Regards,
Inbaraj E
> >
> >
> > Best regards,
> > Krzysztof