linux-kernel - Re: [PATCH 4/5] dmaengine: dw: Ignore burst setting for memory peripherals

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Message-ID: <20200730163122.GW3703480@smile.fi.intel.com>
Date:   Thu, 30 Jul 2020 19:31:22 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Vinod Koul <vkoul@...nel.org>, Viresh Kumar <vireshk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Rob Herring <robh+dt@...nel.org>, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] dmaengine: dw: Ignore burst setting for memory
 peripherals

On Thu, Jul 30, 2020 at 06:45:44PM +0300, Serge Semin wrote:
> According to the DW DMA controller Databook (page 40 "3.5 Memory

Which version of it?

> Peripherals") memory peripherals don't have handshaking interface
> connected to the controller, therefore they can never be a flow
> controller. Since the CTLx.SRC_MSIZE and CTLx.DEST_MSIZE are
> properties valid only for peripherals with a handshaking
> interface, we can freely zero these fields out if the memory peripheral
> is selected to be the source or the destination of the DMA transfers.
> 
> Note according to the databook, length of burst transfers to memory is
> always equal to the number of data items available in a channel FIFO or
> data items required to complete the block transfer, whichever is smaller;
> length of burst transfers from memory is always equal to the space
> available in a channel FIFO or number of data items required to complete
> the block transfer, whichever is smaller.

But does it really matter if you program there something or not?

-- 
With Best Regards,
Andy Shevchenko