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

[Zeng Heng <zengheng4@huawei.com>]

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@huawei.com>


>> |     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.
>