On 8 March 2015 at 12:31, Jean Delvare <[email protected]> wrote: > Hi Ivan, > > On Sat, 07 Mar 2015 22:53:32 +0200, Ivan.khoronzhuk wrote: >> On 03/05/2015 09:46 AM, Jean Delvare wrote: >> > It's not just two tables (I don't expect a lot of BIOSes to provide two >> > tables in practice, and they would have essentially the same format >> > anyway) but more importantly two entry points. The _SM3_ entry point is >> > brand new and most applications (including dmidecode) don't support it >> > yet. It doesn't matter if the kernel itself can parse it, as it passes >> > the raw entry point to applications anyway. >> > >> > It happens that we are introducing this new sysfs raw interface at the >> > same time _SM3_ is being introduced, so we do not have to care about >> > backwards compatibility. Both the kernel and dmidecode will need to be >> > updated to support the new interface, so we can keep things simple and >> > let the kernel expose only the best entry point. >> > >> > If the sysfs raw interface was already present at the time _SM3_ >> > support was being added, then we would have had to present both entry >> > points for backwards compatibility. And if some _SM4_ entry point is >> > ever added in the future with a new format, we will have to export it >> > as a new sysfs attribute so as to not break compatibility. >> > >> > As a summary, I agree that a single entry point file is OK for now, but >> > only because we are lucky that the timing is right. >> >> Despite of timing is right. >> >> The specification doesn't oblige firmware to provide two entry points. >> An implementation may provide either the 32-bit entry point or the 64-bit >> entry point, or both. For compatibility with existing SMBIOS parsers, an >> implementation should provide the 32-bit entry point, but it's not required. > > I expect most implementations will do, as it's trivial to implement. >
Not quite. First of all, some 64-bit ARM systems do not have any system RAM below 4 GB, so there is not way they can implement the 32-bit entry point. Also, the 64-bit entry point does not limit the structure size or the entire table to 64 KB like the 32-bit one does, so it may be necessary to create a whole separate table with a subset of the contents of the real table to stay within limits for the 32-bit entry point. And the 32-bit entry point could well be 3.0 anyway, if it uses any of the new enum values for the data items that were undefined before 3.0. More info here: http://sourceforge.net/p/edk2/mailman/message/33550425/ Regards, Ard. >> you can >> be sure in backward compatibility. But at least for now you can't. >> >> It's obvious, if kernel found two entry points then it can create two >> sysfs attributes. >> But, what kernel should do in case if only one new entry point is present. >> Generate entry point of old version..., sorry but it's bad idea. At >> least because >> where guarantee that we have enough information for this. Only field we >> can bring >> thought entry point versions is magic string _SM*_, and based on it, if util >> don't support new version it can warn. It's used for differ versions and >> there is nothing we can do more. > > I agree that the kernel should not fake an entry point which does not > exist (I'm not sure if you misunderstood me but I never suggested that.) > > -- > Jean Delvare > SUSE L3 Support -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
