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 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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