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

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Message-ID: <305ec65a-bc73-62fc-84a4-4f84ccd1ff1a@tuxon.dev>
Date:   Fri, 15 Sep 2023 08:46:35 +0300
From:   claudiu beznea <claudiu.beznea@...on.dev>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
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



On 14.09.2023 15:13, Geert Uytterhoeven wrote:
> 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.

I'll update it, thanks for pointing it.

> 
>> +                                               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.

I'll have to find the the rationale behind the original timeout. It may be
random, experimental or hardware related.

> 
>> +               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
>