linux-kernel - Re: [PATCH v2 1/4] usb: cdns2: Device side header file for CDNS2 driver

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Message-Id: <acf525da-9a22-472f-abbb-6d1519be8d2a@app.fastmail.com>
Date:   Thu, 20 Apr 2023 11:17:43 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Pawel Laszczak" <pawell@...ence.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Daisy.Barrera@...iusxm.com, Cliff.Holden@...iusxm.com,
        "Tony Lindgren" <tony@...mide.com>,
        "Jean Delvare" <jdelvare@...e.de>, neal_liu@...eedtech.com,
        "Linus Walleij" <linus.walleij@...aro.org>, egtvedt@...fundet.no,
        "Biju Das" <biju.das.jz@...renesas.com>, herve.codina@...tlin.com
Subject: Re: [PATCH v2 1/4] usb: cdns2: Device side header file for CDNS2 driver

On Thu, Apr 20, 2023, at 11:00, Pawel Laszczak wrote:
> Patch defines macros, registers and structures used by
> Device side driver.
>
> Signed-off-by: Pawel Laszczak <pawell@...ence.com>

> +struct cdns2_ep0_regs {
> +	__u8 rxbc;
> +	__u8 txbc;
> +	__u8 cs;
> +	__u8 reserved1[4];
> +	__u8 fifo;
> +	__le32 reserved2[94];
> +	__u8 setupdat[8];
> +	__u8 reserved4[88];
> +	__u8 maxpack;
> +} __packed;

> +struct cdns2_epx_base {
> +	__le16 rxbc;
> +	__u8 rxcon;
> +	__u8 rxcs;
> +	__le16 txbc;
> +	__u8 txcon;
> +	__u8 txcs;
> +} __packed;

> +struct cdns2_epx_regs {
> +	__le32 reserved[2];
> +	struct cdns2_epx_base ep[15];
> +	__u8 reserved2[290];
> +	__u8 endprst;
> +	__u8 reserved3[41];
> +	__le16 isoautoarm;
> +	__u8 reserved4[10];
> +	__le16 isodctrl;
> +	__le16 reserved5;
> +	__le16 isoautodump;
> +	__le32 reserved6;
> +	__le16 rxmaxpack[15];
> +	__le32 reserved7[65];
> +	__le32 rxstaddr[15];
> +	__u8 reserved8[4];
> +	__le32 txstaddr[15];
> +	__u8 reserved9[98];
> +	__le16 txmaxpack[15];
> +} __packed;

Register structures should generally not be __packed, otherwise
any multi-byte registers will be accessed as individual bytes
on architectures that have no unaligned load/store.

If you are worried about struct packing on OABI arm, you can
mark it as both __packed and __aligned(4). Most drivers just
avoid the problem by not defining these as structures but instead
use macros with register offsets.

      Arnd