linux-kernel - Re: [PATCH] clk: sunxi-ng: a523: Mark MBUS clock as critical

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Message-ID: <4383f1ad-2782-4cd9-b21e-55d3a1500e65@arm.com>
Date: Thu, 12 Jun 2025 09:25:53 +0100
From: Andre Przywara <andre.przywara@....com>
To: Chen-Yu Tsai <wens@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
 Jernej Skrabec <jernej.skrabec@...il.com>,
 Samuel Holland <samuel@...lland.org>
Cc: Chen-Yu Tsai <wens@...e.org>, linux-clk@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: sunxi-ng: a523: Mark MBUS clock as critical

Hi Chen-Yu,

thanks for your research on this!

On 07/06/2025 14:50, Chen-Yu Tsai wrote:
> From: Chen-Yu Tsai <wens@...e.org>
> 
> The MBUS serves as the main data bus for various DMA masters in the
> system. If its clock is not enabled, the DMA operations will stall,
> leading to the peripherals stalling or timing out. This has been
> observed as USB or MMC hosts timing out waiting for transactions
> when the clock is automatically disabled by the CCF due to it not
> being used.
> 
> Mark the clock as critical so that it never gets disabled.

Yes, we do this for all the other SoCs, and I somehow missed that for 
the A523.
I am still scratching my head how this worked for me, though, but the 
patch is pretty surely correct:

> Fixes: 74b0443a0d0a ("clk: sunxi-ng: a523: add system mod clocks")
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>

Reviewed-by: Andre Przywara <andre.przywara@....com>

Cheers,
Andre

> ---
>   drivers/clk/sunxi-ng/ccu-sun55i-a523.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/sunxi-ng/ccu-sun55i-a523.c b/drivers/clk/sunxi-ng/ccu-sun55i-a523.c
> index 9efb9fd24b42..1a9a1cb869e2 100644
> --- a/drivers/clk/sunxi-ng/ccu-sun55i-a523.c
> +++ b/drivers/clk/sunxi-ng/ccu-sun55i-a523.c
> @@ -385,7 +385,8 @@ static SUNXI_CCU_MP_DATA_WITH_MUX_GATE_FEAT(mbus_clk, "mbus", mbus_parents,
>   					    0, 0,		/* no P */
>   					    24, 3,	/* mux */
>   					    BIT(31),	/* gate */
> -					    0, CCU_FEATURE_UPDATE_BIT);
> +					    CLK_IS_CRITICAL,
> +					    CCU_FEATURE_UPDATE_BIT);
>   
>   static const struct clk_hw *mbus_hws[] = { &mbus_clk.common.hw };
>