From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Ripard Subject: Re: [PATCH 5/5] RFC spi: sun4i: add DMA support Date: Thu, 2 Jun 2016 10:18:24 +0200 Message-ID: <20160602081824.GH4908@lukather> References: <20160530112610.GJ29837@sirena.org.uk> <20160530150343.GL29837@sirena.org.uk> <20160530155016.GO29837@sirena.org.uk> <20160531132706.GC29837@sirena.org.uk> Reply-To: maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="arYKMy5bKB/hcRo6" Cc: Mark Brown , Geert Uytterhoeven , linux-sunxi , Chen-Yu Tsai , linux-spi , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" To: Michal Suchanek Return-path: Sender: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org Content-Disposition: inline In-Reply-To: List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , List-Id: linux-spi.vger.kernel.org --arYKMy5bKB/hcRo6 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline On Tue, May 31, 2016 at 04:19:28PM +0200, Michal Suchanek wrote: > On 31 May 2016 at 15:27, Mark Brown wrote: > > On Tue, May 31, 2016 at 12:44:54PM +0200, Michal Suchanek wrote: > >> On 30 May 2016 at 17:50, Mark Brown wrote: > >> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote: > > > >> >> It's what the driver did to start with and it was requested to fall > >> >> back to non-DMA in the case DMA is not available. > > > >> > Why? I really can't see any sensible use case for this that doesn't > >> > have a better solution available. > > > >> Of course, the solution is to compile in the DMA driver. > > > >> It's been argued that some drivers which use only short transfers will > >> just work. > > > > With nothing else in the system that needs DMA? It's making the > > performance of the system less reliable for the benefit of a very narrow > > use case. > > Some of the platform devices have dedicated DMA *controller* built > into the device IP so the DMA engine really is optional on many sunxi > devices. Besides SPI you definitely need the DMA engine for audio. You > probably don't need it for storage and graphics. I don't have any idea > if it's used for USB and Ethernet. USB and Ethernet have their own dedicated DMA engines. So currently, the only driver that requires it is the audio codec. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com --arYKMy5bKB/hcRo6--