linux-kernel - Re: [PATCH v1] clk: tegra: clk-dfll: scale force_val with coefficient according to whether cg

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Message-ID: <2464252.ElGaqSPkdT@senjougahara>
Date: Tue, 11 Nov 2025 16:58:05 +0900
From: Mikko Perttunen <mperttunen@...dia.com>
To: pdeschrijver@...dia.com, pgaikwad@...dia.com, mturquette@...libre.com,
 sboyd@...nel.org, thierry.reding@...il.com, jonathanh@...dia.com,
 Alex Tran <alex.t.tran@...il.com>
Cc: linux-clk@...r.kernel.org, linux-tegra@...r.kernel.org,
 linux-kernel@...r.kernel.org, Alex Tran <alex.t.tran@...il.com>
Subject:
 Re: [PATCH v1] clk: tegra: clk-dfll: scale force_val with coefficient
 according to whether cg_scale is set

On Monday, October 27, 2025 8:18 AM Alex Tran wrote:
> force_val was hard coded to use a coefficient of 128,
> regardless of the cg_scale configuration. This should instead match the
> DFLL_PARAMS_CG_SCALE bit, use a coefficient of 128 when
> cg_scale is set, or 1 when not set.
> 
> Signed-off-by: Alex Tran <alex.t.tran@...il.com>
> ---
>  drivers/clk/tegra/clk-dfll.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/tegra/clk-dfll.c b/drivers/clk/tegra/clk-dfll.c
> index 22dc29432eff..3362983eedcf 100644
> --- a/drivers/clk/tegra/clk-dfll.c
> +++ b/drivers/clk/tegra/clk-dfll.c
> @@ -882,7 +882,7 @@ static void dfll_set_frequency_request(struct tegra_dfll *td,
>  {
>  	u32 val = 0;
>  	int force_val;
> -	int coef = 128; /* FIXME: td->cg_scale? */
> +	int coef = td->cg_scale ? 128 : 1;
>  
>  	force_val = (req->lut_index - td->lut_safe) * coef / td->cg;
>  	force_val = clamp(force_val, FORCE_MIN, FORCE_MAX);
> 

Are you seeing some concrete issue that this is fixing? While the current code indeed doesn't look correct, it matches what the downstream kernels do. A quick grep doesn't find any device trees that set 'nvidia,cg-scale', so this patch would change the behavior from 128 to 1, and no longer be aligned with downstream releases.

Mikko