linux-kernel - Re: [PATCH v1 09/16] reset: starfive-jh7100: Add StarFive JH7100 reset driver

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Date:   Tue, 12 Oct 2021 16:31:26 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Emil Renner Berthing <kernel@...il.dk>,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-serial@...r.kernel.org
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Drew Fustini <drew@...gleboard.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Anup Patel <anup.patel@....com>,
        Atish Patra <atish.patra@....com>,
        Matteo Croce <mcroce@...rosoft.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 09/16] reset: starfive-jh7100: Add StarFive JH7100
 reset driver

On Tue, 2021-10-12 at 15:40 +0200, Emil Renner Berthing wrote:
> Add a driver for the StarFive JH7100 reset controller.
> 
> Signed-off-by: Emil Renner Berthing <kernel@...il.dk>
> ---
>  MAINTAINERS                           |   7 ++
>  drivers/reset/Kconfig                 |   8 ++
>  drivers/reset/Makefile                |   1 +
>  drivers/reset/reset-starfive-jh7100.c | 164 ++++++++++++++++++++++++++
>  4 files changed, 180 insertions(+)
>  create mode 100644 drivers/reset/reset-starfive-jh7100.c
> 
[...]
> diff --git a/drivers/reset/reset-starfive-jh7100.c b/drivers/reset/reset-starfive-jh7100.c
> new file mode 100644
> index 000000000000..26bc5b59c1f3
> --- /dev/null
> +++ b/drivers/reset/reset-starfive-jh7100.c
> @@ -0,0 +1,164 @@
[...]
> +static int jh7100_reset_update(struct reset_controller_dev *rcdev,
> +			       unsigned long id, bool assert)
> +{
> +	struct jh7100_reset *data = jh7100_reset_from(rcdev);
> +	unsigned long offset = id / 32;
> +	void __iomem *reg_assert = data->base + JH7100_RESET_ASSERT0 + 4 * offset;
> +	void __iomem *reg_status = data->base + JH7100_RESET_STATUS0 + 4 * offset;
> +	u32 mask = BIT(id % 32);
> +	u32 done = jh7100_reset_asserted[offset] & mask;
> +	unsigned long flags;
> +	u32 value;
> +
> +	if (!assert)
> +		done ^= mask;
> +
> +	spin_lock_irqsave(&data->lock, flags);
> +
> +	value = readl(reg_assert);
> +	if (assert)
> +		value |= mask;
> +	else
> +		value &= ~mask;
> +	writel(value, reg_assert);
> +
> +	do {
> +		value = readl(reg_status) & mask;
> +	} while (value != done);

Looking at the barebox driver, this could loop indefinitely if the
caller forgets to enable the corresponding peripheral clock. Maybe
use readl_poll_timeout() as a safety net.

regards
Philipp