Re: [PATCH v2 2/2] arm_mpam: Update architecture version check for MPAM MSC

[Zeng Heng]

Hi James,

On 2026/5/8 10:26, Zeng Heng wrote:

> > I think its simpler to rule out the unsupported combinations, 
> > something like:
> > | static bool mpam_msc_check_aidr(struct mpam_msc *msc)
> > | {
> > |     u32 rev;
> > |
> > |     rev = __mpam_read_reg(msc, MPAMF_AIDR) & MPAMF_AIDR_ARCH_REV;
> > |
> > |      /*
> > |      * v0.0 and >v2.x aren't supported, but anything else should be 
> > backward
> > |     * compatible to v0.1 or v1.0.
> > |     */
> > |     if (!rev)
> > |         return false;
> > |     if (rev & MPAMF_AIDR_ARCH_MAJOR_REV > MPAM_ARCHITECTURE_V1)
> > |         return false;
> > |

Oops, after more complete version number testing, I found there's an
operator precedence issue here. The correct fix is:

	if ((rev & MPAMF_AIDR_ARCH_MAJOR_REV) > MPAM_ARCHITECTURE_V1)
		return false;

Note that '>' has higher precedence than '&'.


With this fix included:
Tested-by: Zeng Heng <zengheng4@xxxxxxxxxx>


> > |     return true;
> > | }
> >
> > > +    if (!mpam_msc_check_aidr(msc)) {
> > > +        dev_err_once(dev, "MSC does not match MPAM architecture\n");
> > >           return -EIO;
> > >       }
> >
> > I'd like to keep the 'v1.x' in this message - this should help folk 
> > with old stable
> > kernels running on new hardware work out why the feature isn't available.
> > (assuming they have some documentation that says v2.0 in it!)
> >
> > I've rebased this with the above changes, which I'll post shortly for 
> > fixes.
>
> Agreed. Keep the backward compatibility extension for versions
> (compatible with v0.x(x>0) and 1.x), and remove the redundant
> MPAM_ARCHITECTURE_Vx_x macro definitions.
>
> I've verified locally that everything works fine.