Date: Sat, 1 Feb 2020 12:29:48 -0800 From: Conrad Meyer <cem@freebsd.org> To: Dimitry Andric <dim@freebsd.org> Cc: Ian Lepore <ian@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org> Subject: Re: svn commit: r357349 - in head/sys: conf modules/tpm Message-ID: <CAG6CVpU4Dq5XsEjsOaPmdTBoUYj2RyrvH01V%2Bnp87BEQwRROOQ@mail.gmail.com> In-Reply-To: <C4FE2F90-5022-471B-892C-D5F014797169@FreeBSD.org> References: <202001311936.00VJaEDP056807@repo.freebsd.org> <CAG6CVpWy%2BA3MN47GyLoL5jvdT7pMABevg-L9w0o7HpZF9Vq5oQ@mail.gmail.com> <18BC9807-4B4C-482C-AB7E-20F9C7B68F29@FreeBSD.org> <4a87b670557d23181c3a98bc5a65c8c1a42302d3.camel@freebsd.org> <C4FE2F90-5022-471B-892C-D5F014797169@FreeBSD.org>
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On Sat, Feb 1, 2020 at 10:10 AM Dimitry Andric <dim@freebsd.org> wrote: > > On 1 Feb 2020, at 18:48, Ian Lepore <ian@FreeBSD.org> wrote: > > > > So you're going to switch from writing 0 to writing 0xfffffffe, and > > just assume that will work the same? > > ... [Caustic sarcasm elided] > > Hmm, the data sheet says: > > Writes (0000 0001h): Cancel a command > Writes (0000 0000h): Clears field when command has been cancelled > > It seems the other bits in the register are not used for anything. This seems pretty typical for TPM registers (in my limited experience). > So indeed it is probably better to explicitly define these values as 0x0 > and 0x1, and not use ~ or ! operators at all. I would suggest using just a plain 0 for the clear-cancel register write, unless the other bits are actually documented to have meaning, and that meaning is not W1C. My recollection is that many TPM registers only have a single real valid bit, and of those that have more than one, many are W1C. (AND4/OR4 RMW are inappropriate for W1C.) We have at least one AND4/OR4 related bugfix pending in phabricator related to this that I should go ahead and commit: https://reviews.freebsd.org/D23081 . I don't think the ~0x1 (0xff...fe) will actually do anything harmful if the other bits are ignore. But 0 is closer to the data sheet. Please un-disable the Makefile warnings removed in r357349 earlier, too. Thanks, Conrad
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