Messages in this thread | | | Subject | Re: [PATCH] nvme: Add support for Apple 2018+ models | From | Benjamin Herrenschmidt <> | Date | Mon, 15 Jul 2019 20:01:05 +1000 |
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On Mon, 2019-07-15 at 12:28 +0300, Maxim Levitsky wrote: > > To be honest, the spec explicitly states that minimum submission queue entry size is 64 > and minimum completion entry size should be is 16 bytes for NVM command set: > > "Bits 3:0 define the required (i.e., minimum) Submission Queue Entry size when > using the NVM Command Set. This is the minimum entry size that may be used. > The value is in bytes and is reported as a power of two (2^n). The required value > shall be 6, corresponding to 64."
Yes, I saw that :-) Apple seems to ignore this and CC:IOSQES and effectively hard wire a size of 7 (128 bytes) for the IO queue.
> "Bits 3:0 define the required (i.e., minimum) Completion Queue entry size when using > the NVM Command Set. This is the minimum entry size that may be used. The value > is in bytes and is reported as a power of two (2^n). The required value shall be 4, > corresponding to 16." > > Pages 136/137, NVME 1.3d. > > In theory the spec allows for non NVM IO command set, and for which the sq/cq entry sizes can be of any size, > as indicated in SQES/CQES and set in CC.IOCQES/CC.IOSQES, but than most of the spec won't apply to it. > > > Also FYI, values in CC (IOCQES/IOSQES) are for I/O queues, which kind of implies that admin queue, > should always use the 64/16 bytes entries, although I haven't found any explicit mention of that.
Right, and it does on the Apple HW as well.
Cheers, Ben.
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