Le jeudi 26 mars 2015 à 10:11 +0100, Paul Kocialkowski a écrit : > Le jeudi 26 mars 2015 à 09:53 +0100, Hans de Goede a écrit : > > Hi, > > > > On 25-03-15 23:35, Paul Kocialkowski wrote: > > > Le mardi 24 mars 2015 à 09:01 +0100, Hans de Goede a écrit : > > >> Hi, > > >> > > >> On 24-03-15 00:12, Rob Herring wrote: > > >>> On Mon, Mar 23, 2015 at 6:30 AM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > > >>>> Hi, > > >>>> > > >>>> > > >>>> On 22-03-15 22:01, Rob Herring wrote: > > >> > > >> <snip> > > >> > > >>>>> 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 documentation > > >>> requirements. It could be in OpenFirmware specs. Documenting it in the > > >>> 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 could. > > >> > > >> 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 property > > >> 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). > > > > There are already existing users of the serial-number property in devicetree, > > and these already use a free-format string, so AFAICT we have no choice > > but to do the same as the existing users. > > > > But Rob is the expert here, so lets see what Rob has to say. > > > > > 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 > > > > 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. > > > > 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. > > > > > 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. > > > > 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 Oh, and Russell King also seemed to agree back then: http://lkml.iu.edu/hypermail/linux/kernel/1412.0/03318.html Russell, Rob, what are your thoughts on this? > 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 and > > > Linux to start documenting/implementing this. > > > > Thanks for your work on this, lets first hash out to few remaining unclear > > details and then I'm looking forward to your patch set for this. > > > > Regards, > > > > Hans >
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