Re: [PATCH 2/3] hwrng: stm32 - add support for STM32 HW RNG

On 5 October 2015 at 10:22, Daniel Thompson [off-list ref] wrote:

On 4 October 2015 at 11:32, Linus Walleij [off-list ref] wrote:

quoted

On Sat, Oct 3, 2015 at 10:35 PM, Daniel Thompson
3. I took out the datasheet for Nomadik STn8820 and it seems that
the hardware is very similar to what this driver is trying to drive.
CR, SR and DR are in the same place, can you check if you also even
have the PrimeCell magic in the words at offset 0xfe0 thru 0xffc?

The register window for the STM32 RNG is only 0x400 (and I'll fix the
DT for v2 ;-) ) so the STM32 version isn't primecell-like.

quoted

In any case it seems likely that this driver should supercede and replace
drivers/char/hw_random/nomadik-rng.c
still using the PrimeCell bus, and if it doesn't have the PrimeCell
IDs in hardware, this can be specified in the device tree using
arm,primecell-periphid = <0x000805e1>; in the node if need be.
The in-tree driver is dangerously simple and assume too much IMO.

Not sure about this, but I'll take a closer look. There is a certain
family resemblance in the register set but there are significant
differences in data transfer between the Nomadik and STM32 hardware.

Having looked at this I don't really think we would gain very much
from combining these drivers. The cells have different (albeit
slightly similar) register layouts, different ways to transfer data
(16- versus 32-bit) and different ways to report test/report incorrect
clocking. In the case of the RNG the differences therefore span the
entire of its feature set.

I think combining them just results in two drivers that happen to
share a file and I dislike having to add "fake" information to the
devicetree to make it hang together.

Is that convincing for you?


Daniel.
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