Hi Heinrich,
On Sun, 5 Nov 2023 at 14:54, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
On 11/5/23 18:25, Simon Glass wrote:
Hi Heinrich,
On Sun, 5 Nov 2023 at 03:47, Heinrich Schuchardt heinrich.schuchardt@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@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@arm.com Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@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.
Rick, can you help with this? I am thinking of something like this as a top-level node:
rng { compatible = "riscv,zkr"; };
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.
Did you see the other discussion about this? Without a propert driver, there is no way to choose which RNG device is used.
Also the comment is very clear:
/** * struct driver_info - Information required to instantiate a device * * NOTE: Avoid using this except in extreme circumstances, where device tree * is not feasible (e.g. serial driver in SPL where <8KB of SRAM is * available). U-Boot's driver model uses device tree for configuration.
Do we need a build-time warning so people don't forget this?
Regards, Simon