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[216.228.112.22]) by smtp.gmail.com with ESMTPSA id t13sm4085759pjo.13.2019.06.26.17.19.13 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 26 Jun 2019 17:19:13 -0700 (PDT) Date: Wed, 26 Jun 2019 17:19:33 -0700 From: Nicolin Chen To: robin.murphy@arm.com, will.deacon@arm.com Subject: Why doesn't arm-smmu (v2) driver take VA_BITS into consideration? Message-ID: <20190627001932.GA27343@Asurada-Nvidia.nvidia.com> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hello Will/Robin, I am using an Soc that contains arm-smmu v2 engines. I found that the arm-smmu driver reads GR_ID2 register and defines ias and oas of each domain based on the corresponding fields of that GR_ID2. Using my platform for example, it gets 48-bit for all ias and oas, being translated from those fields so I got these 2 stages: Stage-1: 48-bit VA -> 48-bit IPA Stage-2: 48-bit IPA -> 48-bit PA Then the code does below to configure aperture_end to 48-bit: 914 domain->geometry.aperture_end = (1UL << ias) - 1; However, my system configures VA_BITS to 39. So aperture_end==48 is a mismatch comparing to VA_BITS_39. Although the aperture_end is supposed to cap IOVA allocation, this 48-bit cap won't really do the job at all. I saw that arm-smmu-v3 driver takes VA_BITS into consideration: 1765 switch (smmu_domain->stage) { 1766 case ARM_SMMU_DOMAIN_S1: 1767 ias = (smmu->features & ARM_SMMU_FEAT_VAX) ? 1768 ias = min_t(unsigned long, ias, VA_BITS); So I am wondering if it is intentionally designed so by ignoring VA_BITS? Would you please help me understand this a bit? Thank you Nicolin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel