From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anton Bondarenko Subject: Re: [PATCH v3 7/7] spi: imx: defer spi initialization, if DMA engine is pending Date: Sat, 14 Nov 2015 11:03:25 +0100 Message-ID: <564706ED.70102@gmail.com> References: <1446388901-6073-1-git-send-email-anton.bondarenko.sama@gmail.com> <1446388901-6073-8-git-send-email-anton.bondarenko.sama@gmail.com> <20151105085926.GK8526@pengutronix.de> <563B8157.9030104@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, b38343-KZfg59tc24xl57MIdRCFDg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, vladimir_zapolskiy-nmGgyN9QBj3QT0dZR+AlfA@public.gmane.org, jiada_wang-nmGgyN9QBj3QT0dZR+AlfA@public.gmane.org To: Sascha Hauer Return-path: In-Reply-To: <563B8157.9030104-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-spi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: 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 >>> >>> 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 >>> Signed-off-by: Anton Bondarenko >> >> 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-spi" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html