Re: [Qemu-devel] [PATCH v3 for-2.11 3/3] tpm_tis: Return 0 for every register in case of failure mode

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

On 11/14/2017 06:47 PM, Marc-André Lureau wrote:
> Hi
>
> On Tue, Nov 14, 2017 at 10:52 PM, Stefan Berger
> <stefanb@linux.vnet.ibm.com> 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
>> there.
> 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.

    Stefan

>
>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>> ---
>>   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) {
>> --
>> 2.5.5
>>
>
>