linux-kernel - Re: [PATCH] clk: qcom: clk-alpha-pll: Fix pll post div mask when width is not set

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Message-ID: <jsxbyzdamrgrwob2hqzk2ljgu3o6aoyjd42kzyqbvi64dopicl@y4wgaviudiud>
Date: Wed, 25 Sep 2024 19:44:20 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Barnabás Czémán <barnabas.czeman@...nlining.org>
Cc: Bjorn Andersson <andersson@...nel.org>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Satya Priya Kakitapalli <quic_skakitap@...cinc.com>, Konrad Dybcio <konradybcio@...nel.org>, 
	linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: qcom: clk-alpha-pll: Fix pll post div mask when
 width is not set

On Wed, Sep 25, 2024 at 06:09:39PM GMT, Barnabás Czémán wrote:
> Many qcom clock drivers do not have .width set. In that case value of
> (p)->width - 1 will be negative which breaks clock tree. Fix this
> by checking if width is zero, and pass 0 to GENMASK if that's the case.
> 
> Fixes: 2c4553e6c485 ("clk: qcom: clk-alpha-pll: Fix the pll post div mask")
> Signed-off-by: Barnabás Czémán <barnabas.czeman@...nlining.org>
> ---
>  drivers/clk/qcom/clk-alpha-pll.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/qcom/clk-alpha-pll.c b/drivers/clk/qcom/clk-alpha-pll.c
> index f9105443d7dbb104e3cb091e59f43df25999f8b3..1f914bc0af5449ed1fb545d850607138a06fab1a 100644
> --- a/drivers/clk/qcom/clk-alpha-pll.c
> +++ b/drivers/clk/qcom/clk-alpha-pll.c
> @@ -40,7 +40,7 @@
>  
>  #define PLL_USER_CTL(p)		((p)->offset + (p)->regs[PLL_OFF_USER_CTL])
>  # define PLL_POST_DIV_SHIFT	8
> -# define PLL_POST_DIV_MASK(p)	GENMASK((p)->width - 1, 0)
> +# define PLL_POST_DIV_MASK(p)	GENMASK((p)->width ? (p)->width - 1 : 0, 0)

I think the actual problem is in the different commit. Commit
1c3541145cbf ("clk: qcom: support for 2 bit PLL post divider") made
width required, but didn't document it and we did not follow that for a
significant amount of PLLs.

I think a proper fix should be to return 0xf mask if p->width is 0. In
other words, p->width ? p->width-1 : 3

>  # define PLL_ALPHA_MSB		BIT(15)
>  # define PLL_ALPHA_EN		BIT(24)
>  # define PLL_ALPHA_MODE		BIT(25)
> 
> ---
> base-commit: 62f92d634458a1e308bb699986b9147a6d670457
> change-id: 20240925-fix-postdiv-mask-ba47ecd23ea3
> 
> Best regards,
> -- 
> Barnabás Czémán <barnabas.czeman@...nlining.org>
> 

-- 
With best wishes
Dmitry