[PATCH 1/1] rng: detect RISC-V Zkr RNG device in bind method

[Heinrich Schuchardt]

On 11/5/23 18:25, Simon Glass wrote:
> Hi Heinrich,
> 
> On Sun, 5 Nov 2023 at 03:47, Heinrich Schuchardt
> <heinrich.schuchardt at canonical.com> wrote:
>>
>> On 11/4/23 21:42, Simon Glass wrote:
>>> Hi Heinrich,
>>>
>>> On Sat, 4 Nov 2023 at 06:51, Heinrich Schuchardt
>>> <heinrich.schuchardt at canonical.com> wrote:
>>>>
>>>> The existence of devices should be checked in the bind method and not in
>>>> the probe method. Adjust the RISC-V Zkr RNG driver accordingly.
>>>>
>>>> Use ENOENT (and not ENODEV) to signal that the device is not available.
>>>>
>>>> Fixes: ceec977ba1a9 ("rng: Provide a RNG based on the RISC-V Zkr ISA extension")
>>>> Reported-by: Andre Przywara <andre.przywara at arm.com>
>>>> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
>>>> ---
>>>>    drivers/rng/riscv_zkr_rng.c | 34 ++++++++++++++++++++++++++--------
>>>>    1 file changed, 26 insertions(+), 8 deletions(-)
>>>
>>> This device should be in the DT, so you have some control over which
>>> RNG is used.
>>
>> The device-tree provided by QEMU does not contain such a device as Zkr
>> is an ISA extension and not a device. This device-tree is not under the
>> control of the U-Boot project.
> 
> Why do you bring up QEMU? I would expect that it follows the norma dt
> bindings, so it should not be any different from real hardware?

Yes Simon, QEMU follows the normal bindings. If you want to change 
these, please, contribute to the RISC-V working groups or to the Linux 
kernel project.

> 
> Anyway, you could add it. It is just a binding. I believe RISC-V has
> all sorts of isa options which result in different machine features.
> 
> What are you going to do when you want to choose between the ISA RNG
> and a TPM one?

First of all there are different configurations switches for both 
drivers. But of course you can enable both. They will be different 
U-Boot devices. The rng command has a parameter to choose a RNG device 
by device number. This is not different to having two USB drives.

Best regards

Heinrich