linux-kernel - Re: [PATCH 3/9] clk: samsung: gs101: add support for cmu

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Date: Mon, 29 Jan 2024 12:53:00 +0000
From: Peter Griffin <peter.griffin@...aro.org>
To: André Draszik <andre.draszik@...aro.org>
Cc: mturquette@...libre.com, sboyd@...nel.org, robh+dt@...nel.org, 
	krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, 
	linux-kernel@...r.kernel.org, kernel-team@...roid.com, 
	tudor.ambarus@...aro.org, willmcvicker@...gle.com, semen.protsenko@...aro.org, 
	alim.akhtar@...sung.com, s.nawrocki@...sung.com, tomasz.figa@...il.com, 
	cw00.choi@...sung.com, linux-arm-kernel@...ts.infradead.org, 
	linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org, 
	devicetree@...r.kernel.org
Subject: Re: [PATCH 3/9] clk: samsung: gs101: add support for cmu_peric1

On Sat, 27 Jan 2024 at 00:19, André Draszik <andre.draszik@...aro.org> wrote:
>
> CMU_PERIC1 is the clock management unit used for the peric1 block which
> is used for additional USI, I3C and PWM interfaces/busses. Add support
> for muxes, dividers and gates of cmu_peric1, except for
> CLK_GOUT_PERIC1_IP which isn't well described in the datasheet and
> which downstream also ignores (similar to cmu_peric0).
>
> Two clocks have been marked as CLK_IS_CRITICAL for the following
> reason:
>     * disabling them makes it impossible to access any peric1
>       registers, (including those two registers).
>     * disabling gout_peric1_lhm_axi_p_peric1_i_clk sometimes has the
>       additional effect of making the whole system unresponsive.
>
> The clocks marked as CLK_IGNORE_UNUSED need to be kept on until we have
> updated the respective drivers for the following reasons:
>     * gout_peric1_gpio_peric1_pclk is required by the pinctrl
>       configuration. With this clock disabled, reconfiguring the pins
>       (for USI/I2C, USI/UART) will hang during register access.
>       Since pingctrl-samsung doesn't support a clock at the moment, we
>       just keep the kernel from disabling it at boot, until we have an
>       update for samsung-pinctrl, at which point we'll drop the flag.
>     * gout_peric1_sysreg_peric1_pclk needs to be hooked up to
>       sysreg_peric1 in DT which will be done in a followup-patch, at
>       which point we'll drop the special treatment from here. We're
>       adding the flag temporarily here so as to not break the boot (due
>       to pclk otherwise getting disabled).
>
> Signed-off-by: André Draszik <andre.draszik@...aro.org>
>
> ---

Thankyou for being verbose on this reasoning behind CLK_IGNORE_UNUSED
and CLK_IS_CRITICAL flags

Reviewed-by: Peter Griffin <peter.griffin@...aro.org>