linux-kernel - Re: [PATCH v2 1/3] firmware: dmi: Add DMI_PRODUCT

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Date:   Thu, 1 Jun 2017 13:09:40 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Jean Delvare <jdelvare@...e.de>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Wei Yongjun <weiyongjun1@...wei.com>, bbaude@...hat.com,
        mildred-bug.kernel@...dred.fr, barnacs@...tletit.be,
        lvuksta@...il.com, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org, Kelly French <kfrench@...eralhill.net>
Subject: Re: [PATCH v2 1/3] firmware: dmi: Add DMI_PRODUCT_FAMILY
 identification string

On Thu, Jun 01, 2017 at 11:29:26AM +0200, Jean Delvare wrote:
> Hi all,
> 
> Sorry for the late reply.
> 
> On Wed, 17 May 2017 13:25:12 +0300, Mika Westerberg wrote:
> > Sometimes it is more convenient to be able to match a whole family of
> > products, like in case of bunch of Chromebooks based on Intel_Strago to
> > apply a driver quirk instead of quirking each machine one-by-one.
> > 
> > This adds support for DMI_PRODUCT_FAMILY identification string and also
> > exports it to the userspace through sysfs attribute just like the
> > existing ones.
> 
> dmidecode currently provides no direct access to this string. Do you
> think it should?

Yeah, why not. I always just run "dmidecode" without any arguments and
that field is printed nicely among others :)

> > Suggested-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > ---
> >  drivers/firmware/dmi-id.c       | 2 ++
> >  drivers/firmware/dmi_scan.c     | 1 +
> >  include/linux/mod_devicetable.h | 1 +
> >  3 files changed, 4 insertions(+)
> > 
> > diff --git a/drivers/firmware/dmi-id.c b/drivers/firmware/dmi-id.c
> > index 44c01390d035..dc269cb288c2 100644
> > --- a/drivers/firmware/dmi-id.c
> > +++ b/drivers/firmware/dmi-id.c
> > (...)
> > @@ -191,6 +192,7 @@ static void __init dmi_id_init_attr_table(void)
> >  	ADD_DMI_ATTR(product_version,   DMI_PRODUCT_VERSION);
> >  	ADD_DMI_ATTR(product_serial,    DMI_PRODUCT_SERIAL);
> >  	ADD_DMI_ATTR(product_uuid,      DMI_PRODUCT_UUID);
> > +	ADD_DMI_ATTR(product_family,      DMI_PRODUCT_FAMILY);
> 
> Alignment, please!

The patch is already applied and I suppose merged in v4.12-rc3+. Should
I send a fixup patch to fix this?

> 
> >  	ADD_DMI_ATTR(board_vendor,      DMI_BOARD_VENDOR);
> >  	ADD_DMI_ATTR(board_name,        DMI_BOARD_NAME);
> >  	ADD_DMI_ATTR(board_version,     DMI_BOARD_VERSION);
> > diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> > index 54be60ead08f..93f7acdaac7a 100644
> > --- a/drivers/firmware/dmi_scan.c
> > +++ b/drivers/firmware/dmi_scan.c
> > @@ -430,6 +430,7 @@ static void __init dmi_decode(const struct dmi_header *dm, void *dummy)
> >  		dmi_save_ident(dm, DMI_PRODUCT_VERSION, 6);
> >  		dmi_save_ident(dm, DMI_PRODUCT_SERIAL, 7);
> >  		dmi_save_uuid(dm, DMI_PRODUCT_UUID, 8);
> > +		dmi_save_ident(dm, DMI_PRODUCT_FAMILY, 26);
> 
> This field only exists since SMBIOS 2.4. For older implementations, you
> are accessing a random location of the DMI table. Most likely you'll
> hit a character in one of the strings associated with the system
> information structure. In turn this character will be interpreted as a
> DMI string number. With some luck, number will be >= 32, so you'll get
> a non-existent string and dmi_string will return "". But you could hit
> a string terminator (0) and return the 1st string of the structure
> instead (most likely the system manufacturer.)
> 
> Note that the problem is not specific to this field, it is just more
> likely to break because all other fields are defined by SMBIOS 2.0, or
> for the product UUID, SMBIOS 2.1. The fact that all dmi_save_*
> functions blindly assume that the structure is long enough to contain
> all the fields they want to save is problematic. This should be fixed
> separately.

I see. Since you are more familiar with the DMI code, do you have time
to do that or should I try?

Thanks.