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SubjectRe: [PATCH 13/17] staging: wfx: fix endianness of the field 'len'
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On Tuesday 12 May 2020 09:43:34 CEST Geert Uytterhoeven wrote:
> Hi Jerome,
>
> On Mon, May 11, 2020 at 5:53 PM Jerome Pouiller
> <Jerome.Pouiller@silabs.com> wrote:
> > From: Jérôme Pouiller <jerome.pouiller@silabs.com>
> >
> > The struct hif_msg is received from the hardware. So, it declared as
> > little endian. However, it is also accessed from many places in the
> > driver. Sparse complains about that:
> >
> > drivers/staging/wfx/bh.c:88:32: warning: restricted __le16 degrades to integer
> > drivers/staging/wfx/bh.c:88:32: warning: restricted __le16 degrades to integer
> > drivers/staging/wfx/bh.c:93:32: warning: restricted __le16 degrades to integer
> > drivers/staging/wfx/bh.c:93:32: warning: cast to restricted __le16
> > drivers/staging/wfx/bh.c:93:32: warning: restricted __le16 degrades to integer
> > drivers/staging/wfx/bh.c:121:25: warning: incorrect type in argument 2 (different base types)
> > drivers/staging/wfx/bh.c:121:25: expected unsigned int len
> > drivers/staging/wfx/bh.c:121:25: got restricted __le16 [usertype] len
> > drivers/staging/wfx/hif_rx.c:27:22: warning: restricted __le16 degrades to integer
> > drivers/staging/wfx/hif_rx.c:347:39: warning: incorrect type in argument 7 (different base types)
> > drivers/staging/wfx/hif_rx.c:347:39: expected unsigned int [usertype] len
> > drivers/staging/wfx/hif_rx.c:347:39: got restricted __le16 const [usertype] len
> > drivers/staging/wfx/hif_rx.c:365:39: warning: incorrect type in argument 7 (different base types)
> > drivers/staging/wfx/hif_rx.c:365:39: expected unsigned int [usertype] len
> > drivers/staging/wfx/hif_rx.c:365:39: got restricted __le16 const [usertype] len
> > drivers/staging/wfx/./traces.h:195:1: warning: incorrect type in assignment (different base types)
> > drivers/staging/wfx/./traces.h:195:1: expected int msg_len
> > drivers/staging/wfx/./traces.h:195:1: got restricted __le16 const [usertype] len
> > drivers/staging/wfx/./traces.h:195:1: warning: incorrect type in assignment (different base types)
> > drivers/staging/wfx/./traces.h:195:1: expected int msg_len
> > drivers/staging/wfx/./traces.h:195:1: got restricted __le16 const [usertype] len
> > drivers/staging/wfx/debug.c:319:20: warning: restricted __le16 degrades to integer
> > drivers/staging/wfx/secure_link.c:85:27: warning: restricted __le16 degrades to integer
> > drivers/staging/wfx/secure_link.c:85:27: warning: restricted __le16 degrades to integer
>
> Thanks for your patch!
>
> > In order to make Sparse happy and to keep access from the driver easy,
> > this patch declare 'len' with native endianness.
> >
> > On reception of hardware data, this patch takes care to do byte-swap and
> > keep Sparse happy.
>
> Which means sparse can no longer do any checking on the field,
> and new bugs may/will creep in in the future, unnoticed.
>
> > --- a/drivers/staging/wfx/hif_api_general.h
> > +++ b/drivers/staging/wfx/hif_api_general.h
> > @@ -23,7 +23,10 @@
> > #define HIF_COUNTER_MAX 7
> >
> > struct hif_msg {
> > - __le16 len;
> > + // len is in fact little endian. However, it is widely used in the
> > + // driver, so we declare it in native byte order and we reorder just
> > + // before/after send/receive it (see bh.c).
> > + u16 len;
>
> While there's a small penalty associated with always doing the conversion
> on big-endian platforms, it will probably be lost in the noise anyway.

I have made the changes to show you that the code is far more complicated
with a le16... and the result was not as complicated as I expected...

I am going to post a v2.


--
Jérôme Pouiller


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