From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932288AbcFBISj (ORCPT ); Thu, 2 Jun 2016 04:18:39 -0400 Received: from down.free-electrons.com ([37.187.137.238]:40695 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932215AbcFBISh (ORCPT ); Thu, 2 Jun 2016 04:18:37 -0400 Date: Thu, 2 Jun 2016 10:18:24 +0200 From: Maxime Ripard To: Michal Suchanek Cc: Mark Brown , Geert Uytterhoeven , linux-sunxi , Chen-Yu Tsai , linux-spi , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 5/5] RFC spi: sun4i: add DMA support 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> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="arYKMy5bKB/hcRo6" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --arYKMy5bKB/hcRo6 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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. >=20 > 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 --=20 Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com --arYKMy5bKB/hcRo6 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJXT+vQAAoJEBx+YmzsjxAgpWQP+wZvp0BituPVb/OJOWYoeZqR VBEB6N7eDb3mUJ9KwaKa1RyOSgmQTe6pacEFGs9KmaTFArFJsqlBPAsYg0/vHDez 2Je9ZE08kxYj/SoYHqr9bvQnmBEj9Z6LYmdi/rkNET1k0Iuwjs21oCzMjHvJTLLK W85hlDIWgQP2h2b88Sro1vzszE8swtR+iLorRd8WbvqzHi4+H54sNl9rHbDP8JGq hb0J+rOxKOQXDd3qwEhcoUKAebZst63dCsBQoBypUS8W/r0geBmz8nitT92n2kLr kIlnMEY7rsNG2ixPolW0Q5jt1GplkYl6JHx0DOIoB8yTtu62T8twxazxpb5H7Ufv C5mxvx9DUFVaDD56Tl1YB97usfHlhCHwBBh0HCMvfJruL4M6/wREoThxGerpttr5 TQKP/DGZ+f7zVvEUKO5QDkAyjwe3NtbngjFh2zG0EnxQ4+Mv0/vxeh+GXYb3mVbd YyKCKHCoj/+hhrkG6s4z4kAdlyRXqDhUMSn7rIQQcPo8cKTpMnzGmn1yXro/AVic H8oSbx+vwGkWSY9VWpAqNuM5LbB1fBklzT3mTkxk4kesZPjmjyPohVVuwq8vaWIy cA6JE+M0pgw8sYjpr7OQf68RVKeEL+ejMDXeEIo5k2Q3/THJiDs3zKdsstCBOcju veZkT45FDfcTKySKCU5b =64fd -----END PGP SIGNATURE----- --arYKMy5bKB/hcRo6--