From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Kocialkowski Subject: Re: serial atag tag in devicetree ? Date: Thu, 26 Mar 2015 10:11:54 +0100 Message-ID: <1427361114.2342.7.camel@collins> References: <550EA6D8.3090702@redhat.com> <550FF971.407@redhat.com> <551119F1.2060002@redhat.com> <1427322910.26627.15.camel@collins> <5513C926.1010708@redhat.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============2111985156==" Return-path: In-Reply-To: <5513C926.1010708@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: u-boot-bounces@lists.denx.de Sender: "U-Boot" To: Hans de Goede Cc: devicetree , Ian Campbell , U-Boot List-Id: devicetree@vger.kernel.org --===============2111985156== Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-6UOBKDfQXmoy9zsBo+qY" --=-6UOBKDfQXmoy9zsBo+qY Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Le jeudi 26 mars 2015 =C3=A0 09:53 +0100, Hans de Goede a =C3=A9crit : > Hi, >=20 > On 25-03-15 23:35, Paul Kocialkowski wrote: > > Le mardi 24 mars 2015 =C3=A0 09:01 +0100, Hans de Goede a =C3=A9crit : > >> Hi, > >> > >> On 24-03-15 00:12, Rob Herring wrote: > >>> On Mon, Mar 23, 2015 at 6:30 AM, Hans de Goede = wrote: > >>>> Hi, > >>>> > >>>> > >>>> On 22-03-15 22:01, Rob Herring wrote: > >> > >> > >> > >>>>> There is already "serial-number" (a string) which exists for > >>>>> OpenFirmware. Also, "copyright" corresponds to vendor/manufacturer > >>>>> string. Both of these are supported by lshw already. > >>>> > >>>> > >>>> Ok, so if I understand you correctly then you're saying that we > >>>> should set a "serial-number" string property at the dt root level > >>>> and that this may contain pretty much anything, e.g. in the > >>>> sunxi case the full 128 bit SID in hex. > >>> > >>> Right. > >>> > >>>> Is the use of the "serial-number" string property already documented > >>>> somewhere? If not I'll submit a kernel patch to document it. > >>> > >>> Not that I'm aware of. It is something that predates our documentatio= n > >>> requirements. It could be in OpenFirmware specs. Documenting it in th= e > >>> DT bindings does not hurt. > >> > >> Ok. > >> > >>>> And for older kernels we should not set any serial atag (u-boot > >>>> always sets it, so this leaves it at 0) and old kernel users are > >>>> out of luck wrt getting to the serial ? > >>> > >>> If there is sufficient reason to support this on old kernels you coul= d. > >> > >> One problem with supporting this for older kernels is that if a non 0 > >> serial gets shown in /proc/cpuinfo with older atag booted kernels, we > >> should really show the same number in /proc/cpuinfo which means adding > >> code to the kernel to get the devicetree "serial-number" string proper= ty > >> and somehow put that into the 64 bits which we have in /proc/cpuinfo, > >> but given that the "serial-number" string could be hex or decimal or > >> what ever and > 64 bits that will likely require a platform specific > >> solution. All doable, but the question then becomes is this worth the > >> effort ? > > > > After investigating a bit more, I found out that the USB serial number > > is expected to be a string of 32 bytes, so a 128 bit numeric serial > > doesn't fit (it takes 32 bytes for the hex representation of 128 bits, > > so there is no room left for the terminating null byte), hence it makes > > sense to keep a 64 bit limitation for the serial number, if users are > > going to rely on it as USB serial string. Moreover, it seems that > > Android devices are mostly used 64 bit numbers for serial numbers/ > > > > I was initially going to suggest that we set it in stone that serial > > must be 64 numeric bits (as it was in the ATAGs days) and that > > bootloaders would pass it that way to the kernel through device tree > > (with two 32 bits numeric integers), but Hans talked me out of it. > > I just want to expose the situation (especially the USB and Android > > thing) here to double-check that everyone still is convinced that a > > string approach in device tree is best (which is fine with me). >=20 > There are already existing users of the serial-number property in devicet= ree, > and these already use a free-format string, so AFAICT we have no choice > but to do the same as the existing users. >=20 > But Rob is the expert here, so lets see what Rob has to say. >=20 > > This way, users that still want to use the serial passed through device > > tree as a USB serial number will have to use a string of 32 bits, > > including the null terminating byte (which is what I'll suggest for > > sunxi by using only 64 bits for the serial number). > > > > Also, I suggest that we show that serial-number string as-is in cpuinfo > > as well >=20 > We cannot do that because we must guarantee that the serial shown > in cpu info is a 64 bits / 16 hex values (0 padded) number, anything > else would break the kernel <-> userspace API and potentially break > userspace apps. So we must do the devicetree -> serialnumber low/high > -> /proc/cpinfo version to guarantee that this format does not change. >=20 > And as discussed before if you want a non 0 serial in cpuinfo then > the devicetree -> serialnumber low/high should be done in sunxi > specific kernel code, as on sunxi we will know that the string in > devicetree will be a hex value, but we've no such guarantee for > other platforms, so we cannot simply have a generic function to > populate erialnumber low/high from the devicetree serial-number > string. >=20 > > and instead make a string out of the serial ATAG in the kernel > > prior to showing it in cpuinfo (as opposed to translating the string > > coming from device tree to a numeric value that cpuinfo will end up > > showing as a string at the end of the day). Thus, the serial number > > coming from device tree will still be shown in cpuinfo as well and no > > ABI gets broken. >=20 > You're forgetting the userspace <-> kernel ABI here, the serial line > in /proc/cpuinfo is not a free form string it is a 64 bit int shown > as 0 padded hex, and we cannot change that as changing that would be > an ABI break. IMHO this really is all about interpretation. If you consider that the serial is already a *string* and not a hex-representation of a number (which it is when using ATAGs, but has no reason to be in general), then my suggestion will introduce no ABI break. Generally speaking, I found no documentation that indicates that the serial has to be in that format. It just happens to be the case when using ATAGs. Also, I found an email from Rob suggesting he would be fine with wiring the dts serial-number string to cpuinfo: http://lkml.iu.edu/hypermail/linux/kernel/1412.0/02975.html I think it's the most flexible solution and we can think of it as an extension of the current scheme: the serial string will no longer be limited to a hex representation of a number but can become any string. Now I would appreciate it if Rob could weigh-in and state whether he changed his mind on this or not. > > If you're all okay with this, I'll be sending patches to both U-Boot an= d > > Linux to start documenting/implementing this. >=20 > Thanks for your work on this, lets first hash out to few remaining unclea= r > details and then I'm looking forward to your patch set for this. >=20 > Regards, >=20 > Hans --=-6UOBKDfQXmoy9zsBo+qY Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAABAgAGBQJVE81aAAoJEIT9weqP7pUMaL8P/Rqp3jXf9EVeCJdcTYprlMsv ZW+c9/Za6KYVRaAMzuRCuyrC1coCTh0Nux6NXc97A/lvIEBDs4a06S+Z3fpHvQD3 WuK/aBJzNvCmp6mDJKI78eqdXYv7patKgA6I5iJqbo5r7U+CZGbbe9vX6GDmX76M 9gLv9dXHMGgvvHtiNuZ+hOzr84Jk8V4c5UjK/OX46i9ta2gyGmilVG+S4SfIzGZv ILA6h+prXtsUrjNP7l9YSTP4HjvZlfCcXOIeJPpY9oUHWAGtF2382DA1aHYt1j9u OI1oasUCDbPw+Q4FjvVOFZjZt360Yg09T/FIgkL8kJ2FDVX8fBXU0NNM0CmHI5RU 9km/7TPfef9rq/RQhEGzg9mH2pfVLgb83TgrgNJqaAElCvNf0o8n//F6w8cqlaP7 kizXzmvBPiJpt5XncTXs7xWpXBfljtrlDWg4qzPhsCu2qgA4nlbqiPKVixlAqkDA SRcYJ0xiDz8tcgfycoKOO+dA6FjR4kgwBx/W8nahs14/ca7QPspbbYq1xTriMvAU yMjkFg/oBkl/xkf84rSnLTiPXpg1oUpu++mV4WlHJsXMGoK1GxbJptVW5G1Vhhak aZOOYuzhQnxBtClyocLV5sTkXQILmPeBtHoD6lr0PG9vLiLWbaF/9KstnBo1lp7t 6CoGOHC8AWFAi451k+m0 =Om1L -----END PGP SIGNATURE----- --=-6UOBKDfQXmoy9zsBo+qY-- --===============2111985156== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot --===============2111985156==--