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Date: Mon, 11 May 2020 16:45:02 +0300 From: Serge Semin <Sergey.Semin@...kalelectronics.ru> To: Mark Brown <broonie@...nel.org> CC: Serge Semin <fancer.lancer@...il.com>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Vinod Koul <vkoul@...nel.org>, Viresh Kumar <vireshk@...nel.org>, Dan Williams <dan.j.williams@...el.com>, Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, Paul Burton <paulburton@...nel.org>, Ralf Baechle <ralf@...ux-mips.org>, Arnd Bergmann <arnd@...db.de>, Rob Herring <robh+dt@...nel.org>, <linux-mips@...r.kernel.org>, <devicetree@...r.kernel.org>, <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 4/6] dmaengine: dw: Print warning if multi-block is unsupported On Mon, May 11, 2020 at 12:58:13PM +0100, Mark Brown wrote: > On Mon, May 11, 2020 at 05:10:16AM +0300, Serge Semin wrote: > > > Alas linearizing the SPI messages won't help in this case because the DW DMA > > driver will split it into the max transaction chunks anyway. > > That sounds like you need to also impose a limit on the maximum message > size as well then, with that you should be able to handle messages up > to whatever that limit is. There's code for that bit already, so long > as the limit is not too low it should be fine for most devices and > client drivers can see the limit so they can be updated to work with it > if needed. Hmm, this might work. The problem will be with imposing such limitation through the DW APB SSI driver. In order to do this I need to know: 1) Whether multi-block LLP is supported by the DW DMA controller. 2) Maximum DW DMA transfer block size. Then I'll be able to use this information in the can_dma() callback to enable the DMA xfers only for the safe transfers. Did you mean something like this when you said "There's code for that bit already" ? If you meant the max_dma_len parameter, then setting it won't work, because it just limits the SG items size not the total length of a single transfer. So the question is of how to export the multi-block LLP flag from DW DMAc driver. Andy? -Sergey
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