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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
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