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Re: [Qemu-devel] [PATCH v3 for-2.11 3/3] tpm_tis: Return 0 for every reg

From: Stefan Berger
Subject: Re: [Qemu-devel] [PATCH v3 for-2.11 3/3] tpm_tis: Return 0 for every register in case of failure mode
Date: Tue, 14 Nov 2017 20:18:53 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 11/14/2017 06:47 PM, Marc-André Lureau wrote:

On Tue, Nov 14, 2017 at 10:52 PM, Stefan Berger
<address@hidden> wrote:
Rather than returning ~0, return 0 for every register in case of
failure mode. The '0' is better to indicate that there's no device
For most registers, 0 makes more sense. However, I wonder if we
shouldn't just fail to start qemu in this case...

Not convincing me this is 2.11 material either. Does this fix a specific bug?

Yes, SeaBIOS detects the ~0 when it probes and thinks there's a device there. It then hangs trying to set flags and read registers to be able to use the device.


Signed-off-by: Stefan Berger <address@hidden>
  hw/tpm/tpm_tis.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/tpm/tpm_tis.c b/hw/tpm/tpm_tis.c
index fec2fc6..42d647d 100644
--- a/hw/tpm/tpm_tis.c
+++ b/hw/tpm/tpm_tis.c
@@ -545,7 +545,7 @@ static uint64_t tpm_tis_mmio_read(void *opaque, hwaddr addr,
      uint8_t v;

      if (tpm_backend_had_startup_error(s->be_driver)) {
-        return val;
+        return 0;

      switch (offset) {

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