linux-kernel - Re: [PATCH] clk: imx: Fix reparenting of UARTs not associated with sdout

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Date:   Mon, 7 Dec 2020 06:24:38 +0100
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Adam Ford <aford173@...il.com>
Cc:     linux-clk@...r.kernel.org, aford@...conembedded.com,
        charles.steves@...icpd.com, Aisheng Dong <aisheng.dong@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: imx: Fix reparenting of UARTs not associated with
 sdout

Hi Adam,

On Fri, Dec 04, 2020 at 12:31:54PM -0600, Adam Ford wrote:
> The default clock source on i.MX8M Mini and Nano boards use a 24MHz clock,
> but users who need to re-parent the clock source run into issues because
> all the UART clocks are enabled whether or not they're needed by sdout.
> 
> Any attempt to change the parent results in an busy error because the
> clocks have been enabled already.
> 
>   clk: failed to reparent uart1 to sys_pll1_80m: -16
> 
> Instead of pre-initializing all UARTS, scan the device tree to see if UART
> clock is used as stdout before initializing it.  Only enable the UART clock
> if it's needed in order to delay the clock initialization until after the
> re-parenting of the clocks.
> 
> Fixes: 9461f7b33d11c ("clk: fix CLK_SET_RATE_GATE with clock rate protection")
> Suggested-by: Aisheng Dong <aisheng.dong@....com>
> Signed-off-by: Adam Ford <aford173@...il.com>
> 
> diff --git a/drivers/clk/imx/clk.c b/drivers/clk/imx/clk.c
> index 47882c51cb85..6dcc5fbd8f3f 100644
> --- a/drivers/clk/imx/clk.c
> +++ b/drivers/clk/imx/clk.c
> @@ -163,12 +163,18 @@ __setup_param("earlyprintk", imx_keep_uart_earlyprintk,
>  
>  void imx_register_uart_clocks(struct clk ** const clks[])
>  {
> +	struct clk *uart_clk;
>  	if (imx_keep_uart_clocks) {
>  		int i;
>  
>  		imx_uart_clocks = clks;
> -		for (i = 0; imx_uart_clocks[i]; i++)
> -			clk_prepare_enable(*imx_uart_clocks[i]);
> +		for (i = 0; imx_uart_clocks[i]; i++) {
> +			uart_clk = of_clk_get(of_stdout, i);

This looks wrong. imx_uart_clocks is an array containing all clocks that
could possibly be used for an UART. With of_clk_get(of_stdout, i) you
get the nth clock for one specific UART.
What you have to do here is: For each of imx_uart_clocks[] you have to
iterate over all clocks of the of_stdout node.

Sascha

> +			if (IS_ERR(uart_clk))
> +				continue;
> +			clk_prepare_enable(uart_clk);
> +			clk_put(uart_clk);
> +		}
>  	}
>  }
>  
> -- 
> 2.25.1
> 
> 

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