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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4606f26392esm42544726f8f.3.2026.06.16.03.36.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Jun 2026 03:36:53 -0700 (PDT) Date: Tue, 16 Jun 2026 11:36:51 +0100 From: David Laight To: Guo Ren Cc: zhangzhanpeng.jasper@bytedance.com, alex@ghiti.fr, aou@eecs.berkeley.edu, cuiyunhui@bytedance.com, iommu@lists.linux.dev, joro@8bytes.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, luxu.kernel@bytedance.com, palmer@dabbelt.com, pjw@kernel.org, robin.murphy@arm.com, tjeznach@rivosinc.com, will@kernel.org, yuanzhu@bytedance.com Subject: Re: [PATCH v1] iommu/riscv: Support 32-bit register accesses Message-ID: <20260616113651.1048a19a@pumpkin> In-Reply-To: <20260615123821.373248-1-guoren@kernel.org> References: <20260615064855.90316-1-zhangzhanpeng.jasper@bytedance.com> <20260615123821.373248-1-guoren@kernel.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 15 Jun 2026 12:38:17 +0000 Guo Ren wrote: > Hi Zhanpeng Zhang, .. > 3. Only performance-monitoring counters require 64-bit IO access or the > high-low-high do-while retry strategy. For ordinary status and control > MMIO registers, a single read is sufficient. Actually this sequence should be enough for a counter: hi = read_hi(); lo = read_lo(); if (hi != read_hi()) { // Pick a value that happened while doing the reads. hi++; lo = 0; } -- David