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([2600:8803:e7e4:1d00:928b:5d5c:6cd9:1a4]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-735af9bc74csm277033a34.52.2025.05.29.08.33.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 May 2025 08:33:21 -0700 (PDT) Message-ID: Date: Thu, 29 May 2025 10:33:20 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] counter: microchip-tcb-capture: Add DMA support for TC_RAB register reads To: Dharma Balasubiramani , Kamel Bouhara , William Breathitt Gray , Nicolas Ferre , Alexandre Belloni , Claudiu Beznea Cc: linux-arm-kernel@lists.infradead.org, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250528-mchp-tcb-dma-v1-0-083a41fb7b51@microchip.com> <20250528-mchp-tcb-dma-v1-2-083a41fb7b51@microchip.com> Content-Language: en-US From: David Lechner In-Reply-To: <20250528-mchp-tcb-dma-v1-2-083a41fb7b51@microchip.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/28/25 1:13 AM, Dharma Balasubiramani wrote: > Add optional DMA-based data transfer support to read the TC_RAB register, > which provides the next unread captured value from either RA or RB. This > improves performance and offloads CPU when mchp,use-dma-cap is enabled in > the device tree. It looks like this is using DMA to read a single register in the implementation of a sysfs read. Do you have measurements to show the performance difference? I find it hard to believe that this would actually make a significant difference compared to the overhead of the read syscall to read the sysfs attribute.