linux-kernel - Re: [PATCH] dmaengine: sun4i: Set the maximum segment size

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Message-ID: <YsQ25dZ1t4bt7Stg@matsya>
Date:   Tue, 5 Jul 2022 18:34:37 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maxime Ripard <maxime@...no.tech>, dmaengine@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH] dmaengine: sun4i: Set the maximum segment size

On 20-06-22, 22:13, Samuel Holland wrote:
> The sun4i DMA engine supports transfer sizes up to 128k for normal DMA
> and 16M for dedicated DMA, as documented in the A10 and A20 manuals.
> 
> Since this is larger than the default segment size limit (64k), exposing
> the real limit reduces the number of transfers needed for a transaction.
> However, because the device can only report one segment size limit, we
> have to expose the smaller limit from normal DMA.
> 
> One complication is that the driver combines pairs of periodic transfers
> to reduce programming overhead. This only works when the period size is
> at most half of the maximum transfer size. With the default 64k segment
> size limit, this was always the case, but for normal DMA it is no longer
> guaranteed. Skip the optimization if the period is too long; even
> without it, the overhead is less than before.

Applied, thanks

-- 
~Vinod