linux-kernel - RE: [PATCH v2 3/3] platform/x86: dell-wmi: add new dmi keys to bios_to_linux

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Date:   Wed, 10 Jun 2020 12:35:09 +0000
From:   <Mario.Limonciello@...l.com>
To:     <pali@...nel.org>
CC:     <rdunlap@...radead.org>, <y.linux@...itcher.com>,
        <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <mjg59@...f.ucam.org>
Subject: RE: [PATCH v2 3/3] platform/x86: dell-wmi: add new dmi keys to
 bios_to_linux_keycode

> -----Original Message-----
> From: platform-driver-x86-owner@...r.kernel.org <platform-driver-x86-
> owner@...r.kernel.org> On Behalf Of Pali Rohár
> Sent: Wednesday, June 10, 2020 4:45 AM
> To: Limonciello, Mario
> Cc: rdunlap@...radead.org; y.linux@...itcher.com; linux-
> kernel@...r.kernel.org; platform-driver-x86@...r.kernel.org;
> mjg59@...f.ucam.org
> Subject: Re: [PATCH v2 3/3] platform/x86: dell-wmi: add new dmi keys to
> bios_to_linux_keycode
> 
> 
> [EXTERNAL EMAIL]
> 
> On Tuesday 09 June 2020 19:49:18 Mario.Limonciello@...l.com wrote:
> > >
> > > Looking at the last two lines... and for me it looks like that 0x00FF
> > > and 0xFFFF are just "placeholders" or special values for unknown /
> > > custom / unsupported / reserved / special / ... codes.
> > >
> > > It is really suspicious why first 38 values are defined, then there is
> > > gap, then one value 255 and then huge gap to 65535.
> > >
> > > Mario, this looks like some mapping table between internal Dell BIOS
> key
> > > code and standard Linux key code. Are you able to get access to some
> > > documentation which contains explanation of those Dell key numbers?
> > > It could really help us to understand these gaps and what is correct
> > > interpretation of these numbers.
> > >
> >
> > The codes are actually 4 bytes in the table, but in practice nothing
> above the
> > first two bytes is used.
> >
> > Those two called out are special though, here are their meanings:
> >
> > 0x00FF is user programmable function
> > 0xFFFF is no function
> >
> > For the purpose of memory consumption I think it's reasonable to ignore
> the
> > upper 2 bytes and special case these two.
> 
> Thank you for information!
> 
> So 0x00FF is "user programmable" button. Do I understand it correctly
> that Dell/BIOS does not explicitly provide meaning for these buttons,
> they do not have fixed functionality and therefore user should configure
> them as he want?

Correct

> 
> And what does mean "no function"? I do not know what should I imagine if
> I receive key press marked as "no function".

It means no action is expected to occur, should behave like a no-op.  I think
discarding it makes fine sense.

> 
> > > E.g. I remember that pressing Fn+Q or Fn+W on some Dell Latitude
> > > generates code 255, which could prove my thesis about "special codes"
> > > (which are probably not found in e.g. Windows or Linux mapping tables).
> > >
> > > > >  };
> > > > >
> > > > >  /*
> > > > > @@ -503,10 +504,7 @@ static void handle_dmi_entry(const struct
> > > dmi_header *dm, void *opaque)
> > > > >  					&table->keymap[i];
> > > > >
> > > > >  		/* Uninitialized entries are 0 aka KEY_RESERVED. */
> > > > > -		u16 keycode = (bios_entry->keycode <
> > > > > -			       ARRAY_SIZE(bios_to_linux_keycode)) ?
> > > > > -			bios_to_linux_keycode[bios_entry->keycode] :
> > > > > -			KEY_RESERVED;
> > > > > +		u16 keycode = bios_to_linux_keycode[bios_entry->keycode];
> > > > >
> > > > >  		/*
> > > > >  		 * Log if we find an entry in the DMI table that we don't
> > > > >
> > > >
> > > > Something like:
> > > >
> > > > 		u16 keycode;
> > > >
> > > > 		keycode = bios_entry->keycode == 0xffff ? KEY_UNKNOWN :
> > > > 			(bios_entry->keycode <
> > > > 			       ARRAY_SIZE(bios_to_linux_keycode)) ?
> > > > 			bios_to_linux_keycode[bios_entry->keycode] :
> > > > 			KEY_RESERVED;
> > > >
> > > >
> > > >
> > > > Also please fix this:
> > > > (no To-header on input) <>
> > >
> > > Hint: specifying git send-email with '--to' argument instead of '--cc'
> > > should help.
> > >
> > > >
> > > > --
> > > > ~Randy
> > > >