linux-kernel - Re: [PATCH] clk: bcm: rpi: Mark ISP clock as critical

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Message-ID: <3e538ec1-37f6-416c-bc04-6f21a4d31748@broadcom.com>
Date: Tue, 4 Nov 2025 14:20:23 -0800
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Jai Luthra <jai.luthra@...asonboard.com>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Stefan Wahren <wahrenst@....net>,
 Maíra Canal <mcanal@...lia.com>
Cc: linux-clk@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: bcm: rpi: Mark ISP clock as critical

On 10/28/25 04:46, Jai Luthra wrote:
> The ISP clock should also be marked critical to prevent the clock
> framework from disabling it on boot, which can lead to bus lockups when
> the kernel tries to submit buffers to the VC4 ISP firmware.

The commit message suggests that the driver that interfaces with the VC4 
ISP firmware is not ensuring that the clock remains enabled for the 
duration of the transactions. That would be a driver bug, would not it?

> 
> Link: https://github.com/raspberrypi/linux/issues/7100
> Fixes: 919d6924ae9b ("clk: bcm: rpi: Turn firmware clock on/off when preparing/unpreparing")
> Signed-off-by: Jai Luthra <jai.luthra@...asonboard.com>
> ---
>   drivers/clk/bcm/clk-raspberrypi.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/clk/bcm/clk-raspberrypi.c b/drivers/clk/bcm/clk-raspberrypi.c
> index 1a9162f0ae31e330c46f6eafdd00350599b0eede..dcc3ae5fb91650b042d52f02499922786b43afde 100644
> --- a/drivers/clk/bcm/clk-raspberrypi.c
> +++ b/drivers/clk/bcm/clk-raspberrypi.c
> @@ -151,6 +151,7 @@ raspberrypi_clk_variants[RPI_FIRMWARE_NUM_CLK_ID] = {
>   	[RPI_FIRMWARE_ISP_CLK_ID] = {
>   		.export = true,
>   		.minimize = true,
> +		.flags = CLK_IS_CRITICAL,
>   	},
>   	[RPI_FIRMWARE_PIXEL_BVB_CLK_ID] = {
>   		.export = true,
> 
> ---
> base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
> change-id: 20251028-rpi-isp-clk-eb5c48346e51
> 
> Best regards,


-- 
Florian