linux-kernel - Re: [PATCH] drm/msm/dsi: Use division result from div_u64

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Date:   Tue, 07 Sep 2021 15:58:52 -0700
From:   abhinavk@...eaurora.org
To:     Marijn Suijten <marijn.suijten@...ainline.org>
Cc:     phone-devel@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Pavel Dubrova <pashadubrova@...il.com>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dsi: Use division result from div_u64_rem in 7nm
 and 14nm PLL

On 2021-09-06 13:25, Marijn Suijten wrote:
> div_u64_rem provides the result of the divison and additonally the
> remainder; don't use this function to solely calculate the remainder
> while calculating the division again with div_u64.
> 
> A similar improvement was applied earlier to the 10nm pll in
> 5c191fef4ce2 ("drm/msm/dsi_pll_10nm: Fix dividing the same numbers
> twice").
> 
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
Reviewed-by: Abhinav Kumar <abhinavk@...eaurora.org>
> ---
>  drivers/gpu/drm/msm/dsi/phy/dsi_phy_14nm.c | 4 +---
>  drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c  | 4 +---
>  2 files changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_14nm.c
> b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_14nm.c
> index 3c1e2106d962..8905f365c932 100644
> --- a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_14nm.c
> +++ b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_14nm.c
> @@ -213,9 +213,7 @@ static void pll_14nm_dec_frac_calc(struct
> dsi_pll_14nm *pll, struct dsi_pll_conf
>  	DBG("vco_clk_rate=%lld ref_clk_rate=%lld", vco_clk_rate, fref);
> 
>  	dec_start_multiple = div_u64(vco_clk_rate * multiplier, fref);
> -	div_u64_rem(dec_start_multiple, multiplier, &div_frac_start);
> -
> -	dec_start = div_u64(dec_start_multiple, multiplier);
> +	dec_start = div_u64_rem(dec_start_multiple, multiplier, 
> &div_frac_start);
> 
>  	pconf->dec_start = (u32)dec_start;
>  	pconf->div_frac_start = div_frac_start;
> diff --git a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c
> b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c
> index c77c30628cca..1a5abbd9fb76 100644
> --- a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c
> +++ b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c
> @@ -114,9 +114,7 @@ static void dsi_pll_calc_dec_frac(struct
> dsi_pll_7nm *pll, struct dsi_pll_config
> 
>  	multiplier = 1 << FRAC_BITS;
>  	dec_multiple = div_u64(pll_freq * multiplier, divider);
> -	div_u64_rem(dec_multiple, multiplier, &frac);
> -
> -	dec = div_u64(dec_multiple, multiplier);
> +	dec = div_u64_rem(dec_multiple, multiplier, &frac);
> 
>  	if (!(pll->phy->cfg->quirks & DSI_PHY_7NM_QUIRK_V4_1))
>  		config->pll_clock_inverters = 0x28;