Re: [PATCH v4] arm64: cpuinfo: Expose MIDR_EL1 and REVIDR_EL1 to sysfs

[Suzuki K Poulose]

On 13/06/16 18:26, Mark Rutland wrote:
> On Mon, Jun 13, 2016 at 06:08:09PM +0100, Suzuki K Poulose wrote:
> > +/*
> > + * Both MIDR_EL1 and REVIDR_EL1 are 32bit registers. However, per C5.1.1,
> > + * "Principles of the System instruction class encoding" in ARM DDI 0487A.i,
> > + * when a system register is escribed as 32-bit, this only means that the
> > + * upper 32 bits are RES0, not that they will never be made use of. To avoid
> > + * changing the ABI for the future, the values are exported as 64bit values.
> > + */
>
> I see this is a direct copy+paste of my earlier message, typo and all.

> I'd prefer something like the below:
>
> /*
>   * The ARM ARM uses the phrase "32-bit register" to describe a register
>   * whose upper 32 bits are RES0 (per C5.1.1, ARM DDI 0487A.i), however
>   * no statement is made as to whether the upper 32 bits will or will not
>   * be made use of in future, and between ARM DDI 0487A.c and ARM DDI
>   * 0487A.d CLIDR_EL1 was expanded from 32-bit to 64-bit.
>   *
>   * Thus, while both MIDR_EL1 and REVIDR_EL1 are described as 32-bit
>   * registers, we expose them both as 64 bit values to cater for possible
>   * future expansion without an ABI break.
>   */

Sorry about that, will fix it.