linux-kernel - Re: [PATCH v3 3/4] clk: mediatek: Add pcw_chg

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Date:   Wed, 6 Dec 2023 11:38:36 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Daniel Golle <daniel@...rotopia.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Sabrina Dubroca <sd@...asysnail.net>,
        Jianhui Zhao <zhaojh329@...il.com>,
        Chen-Yu Tsai <wenst@...omium.org>,
        "Garmin.Chang" <Garmin.Chang@...iatek.com>,
        Sam Shih <sam.shih@...iatek.com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        James Liao <jamesjj.liao@...iatek.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: [PATCH v3 3/4] clk: mediatek: Add pcw_chg_shift control

Il 06/12/23 01:57, Daniel Golle ha scritto:
> From: Sam Shih <sam.shih@...iatek.com>
> 
> Introduce pcw_chg_shfit control to optionally use that instead of the
> hardcoded PCW_CHG_MASK macro.
> This will needed for clocks on the MT7988 SoC.
> 
> Signed-off-by: Sam Shih <sam.shih@...iatek.com>
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
> ---
> v3: use git --from ...
> v2: no changes
> 
>   drivers/clk/mediatek/clk-pll.c | 5 ++++-
>   drivers/clk/mediatek/clk-pll.h | 1 +
>   2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/mediatek/clk-pll.c b/drivers/clk/mediatek/clk-pll.c
> index 513ab6b1b3229..9f08bc5d2a8a2 100644
> --- a/drivers/clk/mediatek/clk-pll.c
> +++ b/drivers/clk/mediatek/clk-pll.c
> @@ -114,7 +114,10 @@ static void mtk_pll_set_rate_regs(struct mtk_clk_pll *pll, u32 pcw,
>   			pll->data->pcw_shift);
>   	val |= pcw << pll->data->pcw_shift;
>   	writel(val, pll->pcw_addr);
> -	chg = readl(pll->pcw_chg_addr) | PCW_CHG_MASK;
> +	if (pll->data->pcw_chg_shift)
> +		chg = readl(pll->pcw_chg_addr) | BIT(pll->data->pcw_chg_shift);
> +	else
> +		chg = readl(pll->pcw_chg_addr) | PCW_CHG_MASK;
>   	writel(chg, pll->pcw_chg_addr);
>   	if (pll->tuner_addr)
>   		writel(val + 1, pll->tuner_addr);
> diff --git a/drivers/clk/mediatek/clk-pll.h b/drivers/clk/mediatek/clk-pll.h
> index f17278ff15d78..d28d317e84377 100644
> --- a/drivers/clk/mediatek/clk-pll.h
> +++ b/drivers/clk/mediatek/clk-pll.h
> @@ -44,6 +44,7 @@ struct mtk_pll_data {
>   	u32 pcw_reg;
>   	int pcw_shift;
>   	u32 pcw_chg_reg;
> +	int pcw_chg_shift;
>   	const struct mtk_pll_div_table *div_table;
>   	const char *parent_name;
>   	u32 en_reg;

Hmm... no, this is not the best at all and can be improved.

Okay, so, the situation here is that one or some PLL(s) on MT7988 have a different
PCW_CHG_MASK as far as I understand.

Situation here is:
  - Each PLL must be registered to clk-pll
  - Each driver declaring a PLL does exactly so
    - There's a function to register the PLL

You definitely don't want to add a conditional in pll_set_rate(): even though
this is technically not a performance path on the current SoCs (and will probably
never be), it's simply useless to have this (very small) overhead there.

The solution is to:
  - Change that pcw_chg_shift to an unsigned short int type (or u8, your call):
    you don't need 32 bits for this number, as the expected range of this member
    is [0-31], and this can be expressed in just 4 bits (u8 is the smallest though)
  - Add that to function mtk_clk_register_pll_ops()
  - Change mtk_pll_set_rate_regs() to always do
    chg = readl(pll->pcw_chg_addr) | BIT(pll->data->pcw_chg_shift);

Cheers,
Angelo