linux-kernel - Re: [PATCH v1 2/3] clk: tegra: ignore unused vfir clock shared with uartb

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Date:   Thu, 1 Nov 2018 10:41:52 +0200
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Marcel Ziswiler <marcel@...wiler.com>
CC:     <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v1 2/3] clk: tegra: ignore unused vfir clock shared with
 uartb

On Thu, Nov 01, 2018 at 02:52:29AM +0100, Marcel Ziswiler wrote:
> From: Marcel Ziswiler <marcel.ziswiler@...adex.com>
> 
> As UARTB and VFIR share their clock enable bit it is rather unwise for
> the kernel to turn off the VFIR one should that be unused (and
> potentially vice versa but so far there anyway is no VFIR driver).
> 
> Without this patch trying to use UARTB with the regular 8250 driver
> will freeze as soon as ttyS1 is accessed after boot. Luckily, using the
> high-speed Tegra serial driver won't exhibit the issue as clocks are
> dynamically enabled/disabled on every access.
> 
> This has been reproduced both on Apalis T30 as well as Apalis TK1 but
> may be an issue on all Tegra UARTB's which share the clock enable with
> VFIR.
> 

Ah.. the correct fix for this is to initialize the enable_refcnt based on the
hw state. This is done in 9619dba8325fce098bbc9ee2911d1b0150fec0c9 for
periph gate clocks, but obviously also applies to normal periph clocks.

Peter.

> Reported-by: Kory Swain <kory.swain@...pezegroup.com>
> Signed-off-by: Marcel Ziswiler <marcel.ziswiler@...adex.com>
> 
> ---
> 
>  drivers/clk/tegra/clk-tegra-periph.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/tegra/clk-tegra-periph.c b/drivers/clk/tegra/clk-tegra-periph.c
> index cc5275ec2c01..116c74340fb7 100644
> --- a/drivers/clk/tegra/clk-tegra-periph.c
> +++ b/drivers/clk/tegra/clk-tegra-periph.c
> @@ -668,7 +668,7 @@ static struct tegra_periph_init_data periph_clks[] = {
>  	MUX("hda", mux_pllp_pllc_clkm, CLK_SOURCE_HDA, 125, TEGRA_PERIPH_ON_APB, tegra_clk_hda_8),
>  	MUX("hda2codec_2x", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_HDA2CODEC_2X, 111, TEGRA_PERIPH_ON_APB, tegra_clk_hda2codec_2x),
>  	MUX8("hda2codec_2x", mux_pllp_pllc_plla_clkm, CLK_SOURCE_HDA2CODEC_2X, 111, TEGRA_PERIPH_ON_APB, tegra_clk_hda2codec_2x_8),
> -	MUX("vfir", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_VFIR, 7, TEGRA_PERIPH_ON_APB, tegra_clk_vfir),
> +	MUX_FLAGS("vfir", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_VFIR, 7, TEGRA_PERIPH_ON_APB, tegra_clk_vfir, CLK_IGNORE_UNUSED),
>  	MUX("sdmmc1", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_SDMMC1, 14, TEGRA_PERIPH_ON_APB, tegra_clk_sdmmc1),
>  	MUX("sdmmc2", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_SDMMC2, 9, TEGRA_PERIPH_ON_APB, tegra_clk_sdmmc2),
>  	MUX("sdmmc3", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_SDMMC3, 69, TEGRA_PERIPH_ON_APB, tegra_clk_sdmmc3),
> -- 
> 2.14.5
>