Messages in this thread | | | Subject | Re: [tpmdd-devel] tpm: read burstcount from TPM_STS in one 32-bit transaction | From | James Bottomley <> | Date | Tue, 25 Jul 2017 10:36:11 -0700 |
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On Tue, 2017-07-25 at 15:04 +0200, Michal Suchánek wrote: > Hello, > > in commit 9754d45e9970 ("tpm: read burstcount from TPM_STS in one > 32-bit transaction") you change reading of two 8-bit values to one > 32bit read. This is obviously wrong wrt endianess unless the > underlying tpm_tis_read32 does endian conversion.
Some of the bus read primitives do do endianness conversions. The problem is with the SPI attachment, which has unclear endianness. A standard PCI bus attachment uses ioread32() which automatically transforms from a little endian bus to the cpu endianness, however SPI is forced to transfer the bytes one at a time over the serial bus and then transform. The assumption seems to be that the TIS TPM is replying in little endian format when SPI connected.
We can probably get the PPC people to confirm this, I believe they have a SPI attached TPM.
James
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