linux-kernel - Re: [PATCH 07/37] clk: renesas: rzg2l: lock around writes to mux register

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Date:   Thu, 14 Sep 2023 14:13:19 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Claudiu <claudiu.beznea@...on.dev>
Cc:     mturquette@...libre.com, sboyd@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        ulf.hansson@...aro.org, linus.walleij@...aro.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        magnus.damm@...il.com, catalin.marinas@....com, will@...nel.org,
        prabhakar.mahadev-lad.rj@...renesas.com,
        biju.das.jz@...renesas.com, quic_bjorande@...cinc.com,
        arnd@...db.de, konrad.dybcio@...aro.org, neil.armstrong@...aro.org,
        nfraprado@...labora.com, rafal@...ecki.pl,
        wsa+renesas@...g-engineering.com,
        linux-renesas-soc@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH 07/37] clk: renesas: rzg2l: lock around writes to mux register

Hi Claudiu,

On Tue, Sep 12, 2023 at 6:52 AM Claudiu <claudiu.beznea@...on.dev> wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>
> SD MUX output (SD0) is further divided by 4 in G2{L, UL}. The divided
> clock is SD0_DIV4. SD0_DIV4 is registered with CLK_SET_RATE_PARENT which
> means a rate request for it is propagated to the MUX and could reach
> rzg2l_cpg_sd_clk_mux_set_parent() concurrently with the users of SD0.
> Add proper locking to avoid concurrent access on SD MUX set rate
> registers.
>
> Fixes: eaff33646f4cb ("clk: renesas: rzg2l: Add SDHI clk mux support")
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

Thanks for your patch!

> --- a/drivers/clk/renesas/rzg2l-cpg.c
> +++ b/drivers/clk/renesas/rzg2l-cpg.c
> @@ -189,6 +189,7 @@ static int rzg2l_cpg_sd_clk_mux_set_parent(struct clk_hw *hw, u8 index)
>         u32 shift = GET_SHIFT(hwdata->conf);
>         const u32 clk_src_266 = 2;
>         u32 msk, val, bitmask;
> +       unsigned long flags;
>         int ret;
>
>         /*
> @@ -203,25 +204,27 @@ static int rzg2l_cpg_sd_clk_mux_set_parent(struct clk_hw *hw, u8 index)
>          * the index to value mapping is done by adding 1 to the index.
>          */
>         bitmask = (GENMASK(GET_WIDTH(hwdata->conf) - 1, 0) << shift) << 16;
> +       spin_lock_irqsave(&priv->rmw_lock, flags);
>         if (index != clk_src_266) {
>                 writel(bitmask | ((clk_src_266 + 1) << shift), priv->base + off);
>
>                 msk = off ? CPG_CLKSTATUS_SELSDHI1_STS : CPG_CLKSTATUS_SELSDHI0_STS;
>
> -               ret = readl_poll_timeout(priv->base + CPG_CLKSTATUS, val,
> -                                        !(val & msk), 100,
> -                                        CPG_SDHI_CLK_SWITCH_STATUS_TIMEOUT_US);
> -               if (ret) {
> -                       dev_err(priv->dev, "failed to switch clk source\n");
> -                       return ret;
> -               }
> +               ret = readl_poll_timeout_atomic(priv->base + CPG_CLKSTATUS, val,
> +                                               !(val & msk), 100,

According to the read_poll_timeout_atomic() documentation,
delay_us should be less than ~10us.

> +                                               CPG_SDHI_CLK_SWITCH_STATUS_TIMEOUT_US);

CPG_SDHI_CLK_SWITCH_STATUS_TIMEOUT_US = 20 ms, which is a long timeout
for an atomic poll.

> +               if (ret)
> +                       goto unlock;
>         }
>
>         writel(bitmask | ((index + 1) << shift), priv->base + off);
>
> -       ret = readl_poll_timeout(priv->base + CPG_CLKSTATUS, val,
> -                                !(val & msk), 100,
> -                                CPG_SDHI_CLK_SWITCH_STATUS_TIMEOUT_US);
> +       ret = readl_poll_timeout_atomic(priv->base + CPG_CLKSTATUS, val,
> +                                       !(val & msk), 100,
> +                                       CPG_SDHI_CLK_SWITCH_STATUS_TIMEOUT_US);

Likewise.

> +unlock:
> +       spin_unlock_irqrestore(&priv->rmw_lock, flags);
> +
>         if (ret)
>                 dev_err(priv->dev, "failed to switch clk source\n");

The rest LGTM.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds