linux-kernel - Re: [PATCH 01/15] habanalabs: add skeleton driver

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Message-ID: <CAFCwf10jv4aMNefk_1Xj_Tg5Yjg8ekzWtZ94TssfHzaSN5CVAA@mail.gmail.com>
Date:   Sat, 26 Jan 2019 18:24:51 +0200
From:   Oded Gabbay <oded.gabbay@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     gregkh <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ogabbay@...ana.ai
Subject: Re: [PATCH 01/15] habanalabs: add skeleton driver

On Sat, Jan 26, 2019 at 6:06 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Wed, Jan 23, 2019 at 1:01 AM Oded Gabbay <oded.gabbay@...il.com> wrote:
>
> > diff --git a/drivers/misc/habanalabs/include/habanalabs_device_if.h b/drivers/misc/habanalabs/include/habanalabs_device_if.h
> > new file mode 100644
> > index 000000000000..9dbb7077eabd
> > --- /dev/null
> > +++ b/drivers/misc/habanalabs/include/habanalabs_device_if.h
>
> Since this is a apparently a user space ABI, the file should be in
> include/uapi/linux/,
> not in the driver directory.

This is not a user space ABI. This is the ABI between the driver and the F/W.

>
> > +/* must be aligned to 4 bytes */
> > +struct armcp_info {
> > +       struct armcp_sensor sensors[ARMCP_MAX_SENSORS];
> > +       __u8 kernel_version[VERSION_MAX_LEN];
> > +       __u32 reserved[3];
> > +       __u32 cpld_version;
> > +       __u32 infineon_version;
> > +       __u8 fuse_version[VERSION_MAX_LEN];
> > +       __u8 thermal_version[VERSION_MAX_LEN];
> > +       __u8 armcp_version[VERSION_MAX_LEN];
> > +       __u64 dram_size;
> > +};
>
> The compiler will align this to 8 bytes on most architectures, and
> add another padding field before dram_size. Better remove the
> 'reserved' fields, or make them an even number.
I can't do that, because those fields were once used by the F/W and if
I will change the order here, or add/remove those fields then it will
break compatibility with old F/W.

Thanks,
Oded

>
>        Arnd