From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Lechner Subject: Re: [RESEND] spi: davinci: Allow device tree devices to use DMA Date: Mon, 9 Jan 2017 14:40:50 -0600 Message-ID: References: <1483673177-31516-1-git-send-email-david@lechnology.com> <20170109194811.p3if5pzvjjaez2g3@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: nsekhar-l0cyMroinI0@public.gmane.org, khilman-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Mark Brown Return-path: In-Reply-To: <20170109194811.p3if5pzvjjaez2g3-GFdadSzt00ze9xe1eoZjHA@public.gmane.org> Sender: linux-spi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: On 01/09/2017 01:48 PM, Mark Brown wrote: > On Thu, Jan 05, 2017 at 09:26:17PM -0600, David Lechner wrote: > >> This allows SPI devices specified in a device tree to use DMA when the >> master controller. > >> Since device tree is supposed to only describe the hardware, adding such >> a configuration option to device tree would not be acceptable. So, this >> is the best we can do for now to get SPI devices working with DMA. > >> Unfortunately, this excludes the possibility of using one SPI device with >> DMA and one without on the same master. > > Why would you ever want to do that? What would ever make sense about > not using DMA if it's available and the transfer is suitably large, or > conversely why would one want to force DMA even if PIO would be more > performant? I don't particularly want to do that, but that is the way the spi-davinci driver currently works. The choice between DMA or PIO is specified in the platform data on a per-device basis. What I get from your remarks is that this is wrong and it needs to be fixed. If that is so, could someone please point out a driver that does it the right way and I will try to fix it. > >> When I originally submitted this patch, there was some discussion as to whether >> dspi->dma_rx should be changed to return an error rather than being null. > >> However, I prefer it the way it is and don't see a compelling reason to change >> it. > > I don't know what the above comment means, sorry (and don't recall > having seen any earlier versions of this). > FWIW, you can find the previous conversation at https://patchwork.kernel.org/patch/9437901/ -- 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