Re: [PATCH v2 1/6] iommu/vt-d: Setup scalable mode context entry in probe path

[Baolu Lu <baolu.lu@linux.intel.com>]

On 12/12/23 1:38 AM, Jason Gunthorpe wrote:
> On Tue, Dec 05, 2023 at 09:21:58AM +0800, Lu Baolu wrote:
>> +/*
>> + * Get the PASID directory size for scalable mode context entry.
>> + * Value of X in the PDTS field of a scalable mode context entry
>> + * indicates PASID directory with 2^(X + 7) entries.
>> + */
>> +static unsigned long context_get_sm_pds(struct pasid_table *table)
>> +{
>> +	unsigned long pds, max_pde;
>> +
>> +	max_pde = table->max_pasid >> PASID_PDE_SHIFT;
>> +	pds = find_first_bit(&max_pde, MAX_NR_PASID_BITS);
>> +	if (pds < 7)
>> +		return 0;
>> +
>> +	return pds - 7;
> This seems like a convoluted way to write
>    max(ilog2(table-max_pasid) - 7,0)
> 
> ?

Yes. :-)

Something like,

     max(ilog2(table->max_pasid >> PASID_PDE_SHIFT) - 7, 0)

Best regards,
baolu