linux-kernel - Re: [PATCH 2/5] thunderbolt: Obtain PCI slot number from DROM

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Message-ID: <20180910095209.GK14465@lahna.fi.intel.com>
Date:   Mon, 10 Sep 2018 12:52:09 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] thunderbolt: Obtain PCI slot number from DROM

On Sun, Sep 09, 2018 at 11:42:01PM +0200, Lukas Wunner wrote:
> +struct tb_drom_entry_pci {
> +	/* BYTES 0-1 */
> +	struct tb_drom_entry_header header;
> +	/* BYTE 2 */
> +	u8 unknown:5;
> +	u8 slot:3;
> +	/* BYTES 3-10 are only present on PCIe upstream ports */
> +} __packed;

No need for __packed unless you absolutely are certain the compiler does
not do the right thing. When I submitted the network driver, David
Miller explained this to me and I ended up dropping those.

Also use of bitfields is something we should avoid when touching
hardware/firmware records because compiler here can do all sorts of
tricks.

I know the driver is currently using quite many of them but I think it
is good for the new code not to include them anymore.