linux-kernel - Re: [RFC PATCH] ACPI / amba: Skip creating amba device when associated cpu is not online

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Date:   Thu, 27 Jan 2022 13:28:23 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     chenxiang <chenxiang66@...ilicon.com>
Cc:     linux@...linux.org.uk, vkoul@...nel.org,
        linux-arm-kernel@...ts.infradead.org, Suzuki.Poulose@....com,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com
Subject: Re: [RFC PATCH] ACPI / amba: Skip creating amba device when
 associated cpu is not online

Hi Cheng,

I am severely behind in my patch review process and as such will not
be able to start reviewing your work before the week of February 7th.

Thanks,
Mathieu

On Fri, 7 Jan 2022 at 01:47, chenxiang <chenxiang66@...ilicon.com> wrote:
>
> From: Xiang Chen <chenxiang66@...ilicon.com>
>
> If not up all the cpus with command line "maxcpus=x", system will be
> blocked.
> We find that some amba devices such as ETM devices, are associated with
> special cpus, and if the cpu is not up, the register of associated device
> is not allowed to access. BIOS reports all the ETM device nodes and a
> amba device is created for every ETM device, so even if one cpu is not up,
> the amba device will still be created for the associated device, and also
> the register of device (pid and cid) will be accessed when adding amba
> device which will cause the issue.
> To fix it, skip creating amba device if it is associated with a cpu which
> is not online.
>
> Signed-off-by: Xiang Chen <chenxiang66@...ilicon.com>
> ---
>  drivers/acpi/acpi_amba.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>
> diff --git a/drivers/acpi/acpi_amba.c b/drivers/acpi/acpi_amba.c
> index ab8a4e0191b1..2369198f734b 100644
> --- a/drivers/acpi/acpi_amba.c
> +++ b/drivers/acpi/acpi_amba.c
> @@ -16,6 +16,7 @@
>  #include <linux/ioport.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
> +#include <acpi/processor.h>
>
>  #include "internal.h"
>
> @@ -45,6 +46,35 @@ static void amba_register_dummy_clk(void)
>         clk_register_clkdev(amba_dummy_clk, "apb_pclk", NULL);
>  }
>
> +static int acpi_handle_to_cpuid(acpi_handle handle)
> +{
> +       int cpu = -1;
> +       struct acpi_processor *pr;
> +
> +       for_each_possible_cpu(cpu) {
> +               pr = per_cpu(processors, cpu);
> +               if (pr && pr->handle == handle)
> +                       break;
> +       }
> +
> +       return cpu;
> +}
> +
> +static int acpi_dev_get_cpu(struct acpi_device *adev)
> +{
> +       acpi_handle cpu_handle;
> +       acpi_status status;
> +       int cpu;
> +
> +       status = acpi_get_parent(adev->handle, &cpu_handle);
> +       if (ACPI_FAILURE(status))
> +               return -1;
> +       cpu = acpi_handle_to_cpuid(cpu_handle);
> +       if (cpu >= nr_cpu_ids)
> +               return -1;
> +       return cpu;
> +}
> +
>  static int amba_handler_attach(struct acpi_device *adev,
>                                 const struct acpi_device_id *id)
>  {
> @@ -54,11 +84,17 @@ static int amba_handler_attach(struct acpi_device *adev,
>         bool address_found = false;
>         int irq_no = 0;
>         int ret;
> +       int cpu;
>
>         /* If the ACPI node already has a physical device attached, skip it. */
>         if (adev->physical_node_count)
>                 return 0;
>
> +       /* If the cpu associated with the device is not online, skip it. */
> +       cpu = acpi_dev_get_cpu(adev);
> +       if (cpu >= 0 && !cpu_online(cpu))
> +               return 0;
> +
>         dev = amba_device_alloc(dev_name(&adev->dev), 0, 0);
>         if (!dev) {
>                 dev_err(&adev->dev, "%s(): amba_device_alloc() failed\n",
> --
> 2.33.0
>