linux-kernel - Re: [PATCH v2] HID: core: check whether usage page item is after usage id item

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Date:   Thu, 10 Oct 2019 14:16:47 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Candle Sun <candlesea@...il.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        orson.zhai@...soc.com,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Candle Sun <candle.sun@...soc.com>,
        Nianfu Bai <nianfu.bai@...soc.com>
Subject: Re: [PATCH v2] HID: core: check whether usage page item is after
 usage id item

On Thu, Oct 10, 2019 at 5:19 AM Candle Sun <candlesea@...il.com> wrote:
>
> On Thu, Oct 10, 2019 at 2:00 AM Jiri Kosina <jikos@...nel.org> wrote:
> >
> > On Wed, 9 Oct 2019, Nicolas Saenz Julienne wrote:
> >
> > > > diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> > > > index 3eaee2c..3394222 100644
> > > > --- a/drivers/hid/hid-core.c
> > > > +++ b/drivers/hid/hid-core.c
> > > > @@ -35,6 +35,8 @@
> > > >
> > > >  #include "hid-ids.h"
> > > >
> > > > +#define GET_COMPLETE_USAGE(page, id) (((page) << 16) + ((id) & 0xffff))
> > >
> > > Not sure I like the macro. I'd rather have the explicit code. That said, lets
> > > see what Benjamin has to say.
> >
> > Not sure about Benjamin :) but I personally would ask for putting it
> > somewhere into hid.h as static inline.
> >
> > And even if it's for some reason insisted on this staying macro, please at
> > least put it as close to the place(s) it's being used as possible, in
> > order to maintain some code sanity.
> >
> > Thanks,
> >
> > --
> > Jiri Kosina
> > SUSE Labs
> >
>
> Thanks Nicolas and Jiri,
> If macro is not good, I will change it to static function. But the
> funciton is only used in hid-core.c,
> maybe placing it into hid.h is not good?

I would rather use a function too (in hid-core.c, as it's not reused
anywhere else), and we can make it simpler from the caller point of
view (if I am not mistaken):
---
static void concatenate_usage_page(struct hid_parser *parser, int index)
{
    parser->local.usage[index] &= 0xFFFF;
    parser->local.usage[index] |= (parser->global.usage_page & 0xFFFF) << 16;
}

// Which can then be called as:
+       parser->local.usage[parser->local.usage_index] = usage;
+       if (size <= 2)
+               concatenate_usage_page(parser, parser->local.usage_index);
+

// And
        for (i = 0; i < parser->local.usage_index; i++)
-               if (parser->local.usage_size[i] <= 2)
-                       parser->local.usage[i] +=
parser->global.usage_page << 16;
+               if (parser->local.usage_size[i] <= 2) {
+                       concatenate_usage_page(parser, i);
+               }
 }
---

And now that I have written this, the check on the size could also be
very well integrated in concatenate_usage_page().

Cheers,
Benjamin

>
> Regards,
> Candle