[PATCH v2 0/5] ARM: add module autoloading support for crypto modules

[Ard Biesheuvel]

On 15 February 2017 at 20:00, Russell King - ARM Linux
<linux at armlinux.org.uk> wrote:
> On Wed, Jan 11, 2017 at 05:01:53PM +0000, Ard Biesheuvel wrote:
>> This series wires up the crypto modules that use the ARM 32-bit versions of
>> the ARMv8 Crypto Extensions to udev autoloading, by exposing the HWCAP2
>> feature bits via the CPU modalias. This is very similar to the arm64
>> implementation, with the notable exception that ARM has its CPU feature
>> definitions split across HWCAP and HWCAP2.
>
> Note that Aarch64 has:
>
> MODALIAS=cpu:type:aarch64:feature:,0000,0001,0002,0003,0004,0005,0006,0007
>
> which looks weird with the first numeric entry starting with a ','.
>

IIRC this is deliberate, since the udev code matches the feature field
for *nnnn*, which is what the module alias exposes.

> Now as for ARM, yes, we have the hwcap feature split across the two
> (because HWCAP2 didn't exist originally.)  What I'm concerned about
> is that restricting the initial implementation to HWCAP2 bits means
> that we'd have to rework all users if we wanted to include the HWCAP
> bits later on (consider what the change would be to add HWCAP_x
> support to this later on.)
>
> I would much rather we start out now with an offset of 32 on the
> numeric value exposed to userspace, so that should we want to extend
> it to the HWCAP field, we can do so safely.
>

OK, that is easily done.

> While we're stuffing HWCAP2 with new bits, please note that it is
> also limited to 32 bits, just like the HWCAP field is.
>

Yes, I am aware of that. But there aren't /that/ many optional
features that lend themselves for module autoloading.