linux-kernel - Re: [PATCH v3 4/6] clk: renesas: rzv2h: Switch MSTOP configuration to per-bit basis

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Message-ID: <CA+V-a8tO-d35+aPLYoCmC4xKW4cMoNyzM_Vmyw6CzOJjyjj=_g@mail.gmail.com>
Date: Tue, 7 Jan 2025 11:45:54 +0000
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Biju Das <biju.das.jz@...renesas.com>
Cc: Geert Uytterhoeven <geert+renesas@...der.be>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, 
	"linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v3 4/6] clk: renesas: rzv2h: Switch MSTOP configuration to
 per-bit basis

Hi Biju,

On Tue, Jan 7, 2025 at 11:24 AM Biju Das <biju.das.jz@...renesas.com> wrote:
>
> Hi Prabhakar,
>
> Thanks for the patch.
>
> > -----Original Message-----
> > From: Prabhakar <prabhakar.csengg@...il.com>
> > Sent: 02 January 2025 18:19
> > Subject: [PATCH v3 4/6] clk: renesas: rzv2h: Switch MSTOP configuration to per-bit basis
> >
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Switch MSTOP handling from group-based to per-bit configuration to address issues with shared
> > dependencies between module clocks. In the current group-based configuration, multiple module clocks
> > may rely on a single MSTOP bit. When both clocks are turned ON and one is subsequently turned OFF, the
> > shared MSTOP bit will still be set, which is incorrect since the other dependent module clock remains
> > ON.
>
> I guess this statement is incorrect. Still in group-based, mstop bit is controlled by usage count(ref_cnt).
>
It is valid, consider an example say IP-A reuiqres MSTOP bits 8 | 9 |
10 and consider IP-B requires MSTOP bits 10 | 11 | 12 (of the same
MSTOP register say MSTOP1). Now this will be seperate groups having
separate count(ref_cnt). Say you turn ON IP-A module clock and
correspondingly clear the MSTOP bits and similarly now lets turn ON
module clocks for IP-B and clear the MSTOP bits. Now let's say you
want to turn OFF IP-A so you turn OFF module clock and set the MSTOP
bits 8 | 9 | 10. In this case you will now see issues with IP-B as
MSTOP BIT(10) has been set when we turned OFF IP-A block.  This case
is handled by switching refcount on per mstop bit by this patch.

Cheers,
Prabhakar