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Date: Fri, 13 Nov 2015 15:06:55 +0100 From: Mike Looijmans <mike.looijmans@...ic.nl> To: "R, Vignesh" <vigneshr@...com>, Brian Norris <computersforpeace@...il.com> CC: Michal Suchanek <hramrach@...il.com>, Russell King <linux@....linux.org.uk>, <devicetree@...r.kernel.org>, Tony Lindgren <tony@...mide.com>, <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>, Mark Brown <broonie@...nel.org>, <linux-mtd@...ts.infradead.org>, <linux-omap@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org> Subject: Re: [PATCH v3 1/5] spi: introduce mmap read support for spi flash devices On 11-11-15 07:50, R, Vignesh wrote: > Hi Brain, > > On 11/11/2015 4:53 AM, Brian Norris wrote: >> Hi Vignesh, ... >> Also, this API doesn't actually have anything to do with memory mapping. >> It has to do with the de facto standard flash protocol. So I don't think >> mmap belongs in the name; it should be something about flash. (I know of >> at least one other controller that could probably use this API, excpet >> it doesn't use memory mapping to accomplish the accelerated flash read.) The Zynq has a similar way of accessing QSPI flash through a memory map. The memory window is only 16MB, so some form of paging would be needed. It's why I have been following this thread with great interest, since the QSPI performance on the Zynq is way below what it could potentially be. > As far as TI QSPI controller is concerned, the accelerated read happens > via mmap port whereby a predefined memory address space of SoC is > exposed as QSPI mmap region. This region can be accessed like normal > RAM(via memcpy()) and the QSPI controller interface takes care of > fetching data from flash on SPI bus automatically hence, I named it as > above. But, I have no hard feelings if it needs to be generalized to > spi_mtd_read() or something else. I know that on the Zynq, you can even let the DMA controller access the QSPI flash via this memory mapping. The QSPI controller itself doesn't support any DMA at all. If something similar applies to the TI platform (most of the TI procs have nice DMA controllers) one could go one step further and implement a generic DMA-through-mmap access to QSPI flash. Mike. Kind regards, Mike Looijmans System Expert TOPIC Embedded Products Eindhovenseweg 32-C, NL-5683 KH Best Postbus 440, NL-5680 AK Best Telefoon: +31 (0) 499 33 69 79 Telefax: +31 (0) 499 33 69 70 E-mail: mike.looijmans@...icproducts.com Website: www.topicproducts.com Please consider the environment before printing this e-mail Visit us at : Aerospace Electrical Systems Expo Europe which will be held from 17.11.2015 till 19.11.2015, Findorffstrasse 101 Bremen, Germany, Hall 5, stand number C65 http://www.aesexpo.eu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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