On 12 May 2017 at 13:17, Mike Frysinger <vapier@xxxxxxxxxxxx> wrote:
>> Completely untested patch below. Will something like this work?
>>
>> --- a/drivers/char/hw_random/tpm-rng.c
>> +++ b/drivers/char/hw_random/tpm-rng.c
>> @@ -35,7 +35,13 @@ static int tpm_rng_read(struct hwrng *rng, void
>> *data, size_t max, bool wait)
>>
>> static int __init rng_init(void)
>> {
>> - return hwrng_register(&tpm_rng);
>> + struct tpm_chip *tpm_rng_chip = tpm_chip_find_get(TPM_ANY_NUM);
>> + if (tpm_chip) {
>> + tpm_put_ops(tpm_rng_chip);
>> + return hwrng_register(&tpm_rng);
>> + }
>> +
>> + return -ENODEV;
>> }
>> module_init(rng_init);
>
> keep in mind that TPMs are often on slow buses like I2C, so i suspect
> rng_init runs before those have been initialized. so this patch would
> break them.
>
> it would also break if the tpm drivers are modules that don't get
> loaded until later, but tpm-rng is built in. or tpm-rng is loaded
> first.
Hmm. I am not aware of the tpm hardware or driver behavior. Based on
your explanation I see that this patch is not useful. It looks like it
is possible to detect the presence of tpm device and call
hwrng_register once the corresponding driver is loaded.
I leave it to Herbert to decide whether to accept this patch in
current form or not.
Regardless of whether this patch gets accepted or not I can work on a
better fix if you can provide instructions on how to setup and use
tpm. But that will be only after a couple of months.
Regards,
PrasannaKumar
