Date:   Tue, 19 Jan 2021 13:47:49 +0530
From:   Anup Patel <anup@...infault.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Stafford Horne <shorne@...il.com>,
        Karol Gugala <kgugala@...micro.com>,
        Mateusz Holenko <mholenko@...micro.com>,
        Gabriel Somlo <gsomlo@...il.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] drivers/soc/litex: Add restart handler

Hi,

On Tue, Jan 19, 2021 at 1:40 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Let the LiteX SoC Controller register a restart handler, which resets
> the LiteX SoC by writing 1 to CSR_CTRL_RESET_ADDR.
>
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>

We have SBI System Reset Extension (SRST) in upcoming
SBI v0.3 spec. Using this SBI extension, you will not require a
dedicated reboot driver for various projects such as Linux kernel,
U-Boot, EDK2, FreeBSD kernel, etc.

The OpenSBI v0.9 (released yesterday) already has SBI SRST
extension implemented so we will just need platform hooks for
LiteX.

The Linux support for SRST extension is already available on
LKML so far no comments: https://lkml.org/lkml/2020/11/25/6

Regards,
Anup


> ---
> v4:
>   - Drop bogus "a" from description,
>   - Get rid of static litex_soc_ctrl_device and litex_reset_nb
>     instances,
>   - Unregister handler on driver unbind,
>
> v3:
>   - Rebase on top of openrisc/for-next,
>
> v2:
>   - Rebase on top of v5.11-rc1,
>   - Change reset handler priority to recommended default value of 128
>     (was 192).
>
> (v1 was not sent to a mailing list)
> ---
>  drivers/soc/litex/litex_soc_ctrl.c | 42 +++++++++++++++++++++++++++++-
>  1 file changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/soc/litex/litex_soc_ctrl.c b/drivers/soc/litex/litex_soc_ctrl.c
> index da17ba56b7956c84..a7dd5be9fd5bd8ad 100644
> --- a/drivers/soc/litex/litex_soc_ctrl.c
> +++ b/drivers/soc/litex/litex_soc_ctrl.c
> @@ -15,6 +15,11 @@
>  #include <linux/module.h>
>  #include <linux/errno.h>
>  #include <linux/io.h>
> +#include <linux/reboot.h>
> +
> +/* reset register located at the base address */
> +#define RESET_REG_OFF           0x00
> +#define RESET_REG_VALUE         0x00000001
>
>  #define SCRATCH_REG_OFF         0x04
>  #define SCRATCH_REG_VALUE       0x12345678
> @@ -66,8 +71,19 @@ static int litex_check_csr_access(void __iomem *reg_addr)
>
>  struct litex_soc_ctrl_device {
>         void __iomem *base;
> +       struct notifier_block reset_nb;
>  };
>
> +static int litex_reset_handler(struct notifier_block *this, unsigned long mode,
> +                              void *cmd)
> +{
> +       struct litex_soc_ctrl_device *soc_ctrl_dev =
> +               container_of(this, struct litex_soc_ctrl_device, reset_nb);
> +
> +       litex_write32(soc_ctrl_dev->base + RESET_REG_OFF, RESET_REG_VALUE);
> +       return NOTIFY_DONE;
> +}
> +
>  static const struct of_device_id litex_soc_ctrl_of_match[] = {
>         {.compatible = "litex,soc-controller"},
>         {},
> @@ -78,6 +94,7 @@ MODULE_DEVICE_TABLE(of, litex_soc_ctrl_of_match);
>  static int litex_soc_ctrl_probe(struct platform_device *pdev)
>  {
>         struct litex_soc_ctrl_device *soc_ctrl_dev;
> +       int error;
>
>         soc_ctrl_dev = devm_kzalloc(&pdev->dev, sizeof(*soc_ctrl_dev), GFP_KERNEL);
>         if (!soc_ctrl_dev)
> @@ -87,7 +104,29 @@ static int litex_soc_ctrl_probe(struct platform_device *pdev)
>         if (IS_ERR(soc_ctrl_dev->base))
>                 return PTR_ERR(soc_ctrl_dev->base);
>
> -       return litex_check_csr_access(soc_ctrl_dev->base);
> +       error = litex_check_csr_access(soc_ctrl_dev->base);
> +       if (error)
> +               return error;
> +
> +       platform_set_drvdata(pdev, soc_ctrl_dev);
> +
> +       soc_ctrl_dev->reset_nb.notifier_call = litex_reset_handler;
> +       soc_ctrl_dev->reset_nb.priority = 128;
> +       error = register_restart_handler(&soc_ctrl_dev->reset_nb);
> +       if (error) {
> +               dev_warn(&pdev->dev, "cannot register restart handler: %d\n",
> +                        error);
> +       }
> +
> +       return 0;
> +}
> +
> +static int litex_soc_ctrl_remove(struct platform_device *pdev)
> +{
> +       struct litex_soc_ctrl_device *soc_ctrl_dev = platform_get_drvdata(pdev);
> +
> +       unregister_restart_handler(&soc_ctrl_dev->reset_nb);
> +       return 0;
>  }
>
>  static struct platform_driver litex_soc_ctrl_driver = {
> @@ -96,6 +135,7 @@ static struct platform_driver litex_soc_ctrl_driver = {
>                 .of_match_table = of_match_ptr(litex_soc_ctrl_of_match)
>         },
>         .probe = litex_soc_ctrl_probe,
> +       .remove = litex_soc_ctrl_remove,
>  };
>
>  module_platform_driver(litex_soc_ctrl_driver);
> --
> 2.25.1
>
>
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> linux-riscv@...ts.infradead.org
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