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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 5 Jan 2023 13:58:48 -0800
Message-ID: <CAHk-=whxaSHcHeo10JGz3EMJZBfC1LarcrerLos7uHbE1URhtQ@mail.gmail.com>
Subject: Re: [PATCH] tpm: Disable hwrng for TPM 1 if PM_SLEEP is enabled
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Thorsten Leemhuis <regressions@leemhuis.info>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Jason Gunthorpe <jgg@ziepe.ca>, Jan Dabros <jsd@semihalf.com>,
        regressions@lists.linux.dev, LKML <linux-kernel@vger.kernel.org>,
        linux-integrity@vger.kernel.org,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Johannes Altmanninger <aclopte@gmail.com>,
        stable@vger.kernel.org
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On Thu, Jan 5, 2023 at 6:48 AM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> TPM 1's support for its hardware RNG is broken across system suspends,
> due to races or locking issues or something else that haven't been
> diagnosed or fixed yet. These issues prevent the system from actually
> suspending. So disable the driver in this case. Later, when this is
> fixed properly, we can remove this.

How about just keeping it enabled, but not making it a fatal error if
the TPM saving doesn't work? IOW, just print the warning, and then
"return 0" from the suspend function.

I doubt anybody cares, but your patch disables that TPM device just
because PM is *enabled*. That's basically "all the time".

Imagine being on a desktop with a distro kernel that enables suspend -
because that kernel obviously is expected to work on laptops too.
You're never actually going to suspend things on that machine, but
maybe you still want to register it as a source of hw random data?

          Linus