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

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Date:   Sat, 26 Jan 2019 22:14:21 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Oded Gabbay <oded.gabbay@...il.com>
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 5:25 PM Oded Gabbay <oded.gabbay@...il.com> wrote:
>
> 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.

Ah, I see. In that case, you should get rid of all the bitfields and make the
struct members all __le32/__le64/... to make it work on big-endian kernels.

> >
> > > +/* 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.

Ok, I see. Then you should add an explicit padding field and fix the
comment to make the structure match the actual interface.

       Arnd