netdev - Re: [PATCH 13/15] octeontx2-af: Add support for CGX link management

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Message-ID: <CAK8P3a36irQQXSZSACiNDi04AzA2Fb+ZUkWj10mR7Xxu+b0DbA@mail.gmail.com>
Date:   Fri, 28 Sep 2018 10:19:32 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:     Networking <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>, linux-soc@...r.kernel.org,
        lcherian@...vell.com, nmani@...vell.com
Subject: Re: [PATCH 13/15] octeontx2-af: Add support for CGX link management

On Fri, Sep 28, 2018 at 8:09 AM <sunil.kovvuri@...il.com> wrote:
>
> +/* scratchx(0) CSR used for ATF->non-secure SW communication.
> + * This acts as the status register
> + * Provides details on command ack/status, link status, error details
> + */
> +struct cgx_evt_sts {
> +       uint64_t ack:1;
> +       uint64_t evt_type:1;            /* cgx_evt_type */
> +       uint64_t stat:1;                /* cgx_stat */
> +       uint64_t id:6;                  /* cgx_evt_id/cgx_cmd_id */
> +       uint64_t reserved:55;
> +};
> +
> +/* Response to command IDs with command status as CGX_STAT_FAIL
> + *
> + * Not applicable for commands :
> + * CGX_CMD_LINK_BRING_UP/DOWN/CGX_EVT_LINK_CHANGE
> + * check struct cgx_lnk_sts comments
> + */
> +struct cgx_err_sts_s {
> +       uint64_t reserved1:9;
> +       uint64_t type:10;               /* cgx_error_type */
> +       uint64_t reserved2:35;
> +};
> +
> +/* Response to cmd ID as CGX_CMD_GET_FW_VER with cmd status as
> + * CGX_STAT_SUCCESS
> + */
> +struct cgx_ver_s {
> +       uint64_t reserved1:9;
> +       uint64_t major_ver:4;
> +       uint64_t minor_ver:4;
> +       uint64_t reserved2:47;
> +};

>From what I can tell, you pass these structures to the device, so they
are a binary interface. I don't think you can rely on bitfields to work
correctly here, they are generally not portable and I wouldn't rely
on them doing the right thing if you build a big-endian kernel.

It's better to use bitmasks on a u64 value instead to make it obviously
portable.

       Arnd