linux-kernel - Re: [PATCH v4 13/24] fpga: region: add compat

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Date:   Wed, 28 Feb 2018 16:55:15 -0600
From:   Alan Tull <atull@...nel.org>
To:     Wu Hao <hao.wu@...el.com>
Cc:     Moritz Fischer <mdf@...nel.org>, linux-fpga@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org, "Kang, Luwei" <luwei.kang@...el.com>,
        "Zhang, Yi Z" <yi.z.zhang@...el.com>
Subject: Re: [PATCH v4 13/24] fpga: region: add compat_id support

On Tue, Feb 13, 2018 at 3:24 AM, Wu Hao <hao.wu@...el.com> wrote:

Hi Hao,

> This patch introduces a compat_id member and sysfs interface for each
> fpga-region, e.g userspace applications could read the compat_id
> from the sysfs interface for compatibility checking before PR.
>
> Signed-off-by: Wu Hao <hao.wu@...el.com>
> ---
>  Documentation/ABI/testing/sysfs-class-fpga-region |  5 +++++
>  drivers/fpga/fpga-region.c                        | 19 +++++++++++++++++++
>  include/linux/fpga/fpga-region.h                  | 13 +++++++++++++
>  3 files changed, 37 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-class-fpga-region
>
> diff --git a/Documentation/ABI/testing/sysfs-class-fpga-region b/Documentation/ABI/testing/sysfs-class-fpga-region
> new file mode 100644
> index 0000000..419d930
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-class-fpga-region
> @@ -0,0 +1,5 @@
> +What:          /sys/class/fpga_region/<region>/compat_id
> +Date:          February 2018
> +KernelVersion: 4.16
> +Contact:       Wu Hao <hao.wu@...el.com>
> +Description:   FPGA region id for compatibility check.
> diff --git a/drivers/fpga/fpga-region.c b/drivers/fpga/fpga-region.c
> index 660a91b..babec96 100644
> --- a/drivers/fpga/fpga-region.c
> +++ b/drivers/fpga/fpga-region.c
> @@ -162,6 +162,24 @@ int fpga_region_program_fpga(struct fpga_region *region)
>  }
>  EXPORT_SYMBOL_GPL(fpga_region_program_fpga);
>
> +static ssize_t compat_id_show(struct device *dev,
> +                             struct device_attribute *attr, char *buf)
> +{
> +       struct fpga_region *region = to_fpga_region(dev);

This looks good, but not all users of FPGA are going to use compat_id.
How would you feel about making it a pointer in struct fpga_region?
With compat_id as a pointer, could check for non-null compat_id
pointer and return an error if it wasn't initialized.

> +
> +       return sprintf(buf, "%016llx%016llx\n",
> +                      (unsigned long long)region->compat_id.id_h,
> +                      (unsigned long long)region->compat_id.id_l);
> +}
> +
> +static DEVICE_ATTR_RO(compat_id);
> +
> +static struct attribute *fpga_region_attrs[] = {
> +       &dev_attr_compat_id.attr,
> +       NULL,
> +};
> +ATTRIBUTE_GROUPS(fpga_region);
> +
>  int fpga_region_register(struct fpga_region *region)
>  {
>         struct device *dev = region->parent;
> @@ -226,6 +244,7 @@ static int __init fpga_region_init(void)
>         if (IS_ERR(fpga_region_class))
>                 return PTR_ERR(fpga_region_class);
>
> +       fpga_region_class->dev_groups = fpga_region_groups;
>         fpga_region_class->dev_release = fpga_region_dev_release;
>
>         return 0;
> diff --git a/include/linux/fpga/fpga-region.h b/include/linux/fpga/fpga-region.h
> index 423c87e..bf97dcc 100644
> --- a/include/linux/fpga/fpga-region.h
> +++ b/include/linux/fpga/fpga-region.h
> @@ -6,6 +6,17 @@
>  #include <linux/fpga/fpga-bridge.h>
>
>  /**
> + * struct fpga_region_compat_id - FPGA Region id for compatibility check
> + *
> + * @id_h: high 64bit of the compat_id
> + * @id_l: low 64bit of the compat_id
> + */
> +struct fpga_region_compat_id {
> +       u64 id_h;
> +       u64 id_l;

I guess each user will choose how to define these bits.

> +};
> +
> +/**
>   * struct fpga_region - FPGA Region structure
>   * @dev: FPGA Region device
>   * @parent: parent device
> @@ -13,6 +24,7 @@
>   * @bridge_list: list of FPGA bridges specified in region
>   * @mgr: FPGA manager
>   * @info: FPGA image info
> + * @compat_id: FPGA region id for compatibility check.
>   * @priv: private data
>   * @get_bridges: optional function to get bridges to a list
>   * @groups: optional attribute groups.
> @@ -24,6 +36,7 @@ struct fpga_region {
>         struct list_head bridge_list;
>         struct fpga_manager *mgr;
>         struct fpga_image_info *info;
> +       struct fpga_region_compat_id compat_id;

Here it would be a pointer instead.

Alan

>         void *priv;
>         int (*get_bridges)(struct fpga_region *region);
>         const struct attribute_group **groups;
> --
> 2.7.4
>