linux-kernel - Re: [PATCH 2/2] counter: microchip-tcb-capture: Add DMA support for TC

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Message-ID: <b45ea46b-3e17-4cb9-8e69-9eea0a3f8241@baylibre.com>
Date: Thu, 29 May 2025 10:33:20 -0500
From: David Lechner <dlechner@...libre.com>
To: Dharma Balasubiramani <dharma.b@...rochip.com>,
 Kamel Bouhara <kamel.bouhara@...tlin.com>,
 William Breathitt Gray <wbg@...nel.org>,
 Nicolas Ferre <nicolas.ferre@...rochip.com>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>,
 Claudiu Beznea <claudiu.beznea@...on.dev>
Cc: linux-arm-kernel@...ts.infradead.org, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] counter: microchip-tcb-capture: Add DMA support for
 TC_RAB register reads

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.