linux-kernel - Re: [PATCH v8 01/21] pinctrl: tegra: Fix write barrier placement in pmx

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Date:   Fri, 9 Aug 2019 14:38:54 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com, tglx@...utronix.de,
        jason@...edaemon.net, marc.zyngier@....com,
        linus.walleij@...aro.org, stefan@...er.ch, mark.rutland@....com
Cc:     pdeschrijver@...dia.com, pgaikwad@...dia.com, sboyd@...nel.org,
        linux-clk@...r.kernel.org, linux-gpio@...r.kernel.org,
        jckuo@...dia.com, josephl@...dia.com, talho@...dia.com,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        mperttunen@...dia.com, spatra@...dia.com, robh+dt@...nel.org,
        devicetree@...r.kernel.org, rjw@...ysocki.net,
        viresh.kumar@...aro.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v8 01/21] pinctrl: tegra: Fix write barrier placement in
 pmx_writel

09.08.2019 2:46, Sowjanya Komatineni пишет:
> pmx_writel uses writel which inserts write barrier before the
> register write rather.
> 
> This patch has fix to replace writel with writel_relaxed followed
> by a write barrier to ensure write operation before the barrier
> is completed for successful pinctrl change.
> 
> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
> ---
>  drivers/pinctrl/tegra/pinctrl-tegra.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pinctrl/tegra/pinctrl-tegra.c b/drivers/pinctrl/tegra/pinctrl-tegra.c
> index e3a237534281..982ee634b3b1 100644
> --- a/drivers/pinctrl/tegra/pinctrl-tegra.c
> +++ b/drivers/pinctrl/tegra/pinctrl-tegra.c
> @@ -32,7 +32,9 @@ static inline u32 pmx_readl(struct tegra_pmx *pmx, u32 bank, u32 reg)
>  
>  static inline void pmx_writel(struct tegra_pmx *pmx, u32 val, u32 bank, u32 reg)
>  {
> -	writel(val, pmx->regs[bank] + reg);
> +	writel_relaxed(val, pmx->regs[bank] + reg);
> +	/* make sure pinmux register write completed */
> +	wmb();
>  }
>  
>  static int tegra_pinctrl_get_groups_count(struct pinctrl_dev *pctldev)
> 

But this only ensures that CPU have sent the write to the APB BUS and
not that the write actually taken into effect? I'm a bit paranoid when
it comes to a cross-domain synchronization things.

Any ways it looks better than it was before.

Reviewed-by: Dmitry Osipenko <digetx@...il.com>