linux-kernel - Re: [PATCH v2 08/13] dmaengine: at_xdmac: Move the free desc to the tail of the desc list

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Message-ID: <YbcLjrMF0YrCVgjc@matsya>
Date:   Mon, 13 Dec 2021 14:29:58 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Tudor.Ambarus@...rochip.com
Cc:     Ludovic.Desroches@...rochip.com, richard.genoud@...il.com,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        Nicolas.Ferre@...rochip.com, alexandre.belloni@...tlin.com,
        mripard@...nel.org, linux-arm-kernel@...ts.infradead.org,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v2 08/13] dmaengine: at_xdmac: Move the free desc to the
 tail of the desc list

On 13-12-21, 08:51, Tudor.Ambarus@...rochip.com wrote:
> Hi, Vinod,
> 
> On 12/13/21 10:07 AM, Vinod Koul wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > On 25-11-21, 11:00, Tudor Ambarus wrote:
> >> So that we don't use the same desc over and over again.
> > 
> > Please use full para in the changelog and not a continuation of the
> > patch title!
> 
> Ok, will add a better commit description. Here and in other patches where
> your comment applies.

Great!

> > 
> > and why is wrong with using same desc over and over? Any benefits of not
> > doing so?
> 
> Not wrong, but if we move the free desc to the tail of the list, then the
> sequence of descriptors is more track-able in case of debug. You would
> know which descriptor should come next and you could easier catch
> concurrency over descriptors for example. I saw virt-dma uses
> list_splice_tail_init() as well, I found it a good idea, so I thought to
> follow the core driver.

Okay, I would be good to add this motivation in the change log. I am
sure after few you would also wonder why you did this change :)

-- 
~Vinod