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Date: Sat, 14 Nov 2015 11:03:25 +0100 From: Anton Bondarenko <anton.bondarenko.sama@...il.com> To: Sascha Hauer <s.hauer@...gutronix.de> Cc: broonie@...nel.org, b38343@...escale.com, linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, vladimir_zapolskiy@...tor.com, jiada_wang@...tor.com Subject: Re: [PATCH v3 7/7] spi: imx: defer spi initialization, if DMA engine is pending On 05.11.2015 17:18, Anton Bondarenko wrote: > On 05.11.2015 09:59, Sascha Hauer wrote: >> On Sun, Nov 01, 2015 at 03:41:41PM +0100, Anton Bondarenko wrote: >>> From: Anton Bondarenko <anton_bondarenko@...tor.com> >>> >>> If SPI device supports DMA mode, but DMA controller is not yet >>> available due to e.g. a delay in the corresponding kernel module >>> initialization, retry to initialize SPI driver later on instead of >>> falling back into PIO only mode. >>> >>> Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com> >>> Signed-off-by: Anton Bondarenko <anton_bondarenko@...tor.com> >> >> Ok, so 6/7 is only part of the deferral story. Maybe squash the two >> patches into one? >> >> Sascha > > I would like to keep these two changes separately since I have a small > concern about this exact change. > > Let's assume such scenario: > - ECSPI configured to use DMA in device tree and DMA controller > description specified. But there is no driver for this controller in > kernel. > In this case dmaengine will always return -EDEFER and driver postpone > spi-imx initialization. So finally there will be no SPI support even in > PIO mode. > Or for example spi-imx will be compiled into kernel, but DMA controller > driver will be on SPI-NOR based rootfs. > > So the question is "Should we allow user to use incorrect combination of > kernel configuration and DTS and work at least with some limitation?" Or > should we try to guarantee device tree file requirement to use DMA. > > Any thoughts? > > Regards, Anton Does anyone has other comments regarding this commit? Regards, Anton -- 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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