On Mon, Jun 18, 2018 at 2:37 PM, Elliott, Robert (Persistent Memory) <elliott@xxxxxxx> wrote: > > >> -----Original Message----- >> From: Dan Williams [mailto:dan.j.williams@xxxxxxxxx] >> Sent: Monday, June 18, 2018 2:47 PM >> To: Kani, Toshi <toshi.kani@xxxxxxx> >> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-nvdimm@xxxxxxxxxxxx; Moore, Robert >> <robert.moore@xxxxxxxxx>; Li, Juston <juston.li@xxxxxxxxx>; >> rjw@xxxxxxxxxxxxx; linux-acpi@xxxxxxxxxxxxxxx; Elliott, Robert (Persistent >> Memory) <elliott@xxxxxxx> >> Subject: Re: [PATCH v3 1/2] acpi/nfit: Update nfit driver to comply with >> ACPI 6.1 >> >> On Mon, Jun 18, 2018 at 12:39 PM, Kani, Toshi <toshi.kani@xxxxxxx> wrote: >> > On Mon, 2018-06-18 at 12:01 -0700, Dan Williams wrote: >> >> On Mon, Apr 25, 2016 at 2:43 PM Toshi Kani <toshi.kani@xxxxxxx> wrote: >> >> > >> >> > ACPI 6.1, Table 5-133, updates NVDIMM Control Region Structure >> >> > as follows. >> >> > - Valid Fields, Manufacturing Location, and Manufacturing Date >> >> > are added from reserved range. No change in the structure size. >> >> > - IDs (SPD values) are stored as arrays of bytes (i.e. big-endian >> >> > format). The spec clarifies that they need to be represented >> >> > as arrays of bytes as well. >> >> > >> >> >> >> Circling back on this a couple years too late... where are you reading >> >> this "arrays of bytes" note. As far as I can see this is wrong. JEDEC >> >> says that vendor id is stored LSB of the id is stored at the lowest >> >> byte in SPD, which is little endian. So it seems Linux has showing the >> >> incorrect value for a long time now. >> > >> > This follows ACPI 6.2a section 5.2.25.10 NVDIMM Representation Format, >> > which Robert cited in his comment below: >> > https://patchwork.kernel.org/patch/10237609/ >> >> Right, the representation format has the fields big-endian for some >> reason, but the individual values for sysfs should be show >> little-endian as far as I can see. What am I missing? > > In practice, the serial numbers from three major DDR4 DIMM manufacturers > are being assigned as big-endian, like in this set of NVDIMM-Ns: > /sys/bus/nd/devices/nmem0/nfit/serial:0x122f8255 > /sys/bus/nd/devices/nmem1/nfit/serial:0x122f7f5e > /sys/bus/nd/devices/nmem2/nfit/serial:0x122f818f > /sys/bus/nd/devices/nmem3/nfit/serial:0x122f821c > /sys/bus/nd/devices/nmem4/nfit/serial:0x122f817e > /sys/bus/nd/devices/nmem5/nfit/serial:0x122f81cd > /sys/bus/nd/devices/nmem6/nfit/serial:0x122f821e > /sys/bus/nd/devices/nmem7/nfit/serial:0x122f819b > /sys/bus/nd/devices/nmem8/nfit/serial:0x122f81a2 > /sys/bus/nd/devices/nmem9/nfit/serial:0x122f8198 > /sys/bus/nd/devices/nmem10/nfit/serial:0x122f8193 > /sys/bus/nd/devices/nmem11/nfit/serial:0x122f7f58 > /sys/bus/nd/devices/nmem12/nfit/serial:0x122f81cb > /sys/bus/nd/devices/nmem13/nfit/serial:0x122f8181 > /sys/bus/nd/devices/nmem14/nfit/serial:0x122f8210 > /sys/bus/nd/devices/nmem15/nfit/serial:0x122f821f > > and this set of regular DIMMs: > 396851B4 > 3968134C > 396852DA > 396850AB > 39685A13 > 39685317 > 396852DD > 396852D9 Let's take something simple like Vendor ID. What is the Vendor ID for these DIMMs and what does Linux print in sysfs? > Of the possible approaches for the sysfs nfit field decodes: > fixed big-endian: > matches printed label content (text and barcode) > matches ACPI display advice for management tools > probably matches SMBIOS Serial Number string format (although > that depends on the system firmware) > requires user to know that this OS uses big-endian > has been upstream for a while now > fixed little-endian: > harder to see that cd812f12 matches 122f81cd seen elsewhere > harder to notice that B4516839 is a peer of 4C136839 > might match other little-endian-only OSes > requires user to know that this OS uses little-endian > native endian: > most confusing > config/status files referencing the DIMMs are not portable > requires user to know that this OS uses native endianness > requires user to know the CPU endianness > was upstream several years ago The time upstream is painful, but if Linux is needlessly swizzling the bits this needs to be fixed. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
