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Message-ID: <11b4b1db-2fde-413c-a203-0734bc18f4f7@linux.intel.com>
Date:   Tue, 12 Dec 2023 13:34:19 +0800
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Cc:     baolu.lu@linux.intel.com, Joerg Roedel <joro@8bytes.org>,
        Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Kevin Tian <kevin.tian@intel.com>, iommu@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/6] iommu/vt-d: Setup scalable mode context entry in
 probe path
Content-Language: en-US
To:     Jason Gunthorpe <jgg@ziepe.ca>
References: <20231205012203.244584-1-baolu.lu@linux.intel.com>
 <20231205012203.244584-2-baolu.lu@linux.intel.com>
 <20231211173826.GE1489931@ziepe.ca>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <20231211173826.GE1489931@ziepe.ca>
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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