From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfram Sang Subject: Re: [PATCH 2/5] i2c: sh_mobile: add DMA support Date: Thu, 11 Dec 2014 08:37:27 +0100 Message-ID: <20141211073727.GA1252@katana> References: <1415355104-2031-1-git-send-email-wsa@the-dreams.de> <20141210080155.GA1148@katana> <10746939.zT8Pinqvll@avalon> <20141210142314.GB8247@katana> <20141211050226.GJ16827@intel.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="YZ5djTAD1cGYuMQK" Return-path: Content-Disposition: inline In-Reply-To: <20141211050226.GJ16827@intel.com> Sender: linux-sh-owner@vger.kernel.org To: Vinod Koul Cc: Laurent Pinchart , Magnus Damm , Geert Uytterhoeven , Linux I2C , Linux-sh list , Simon Horman , dmaengine@vger.kernel.org List-Id: linux-i2c@vger.kernel.org --YZ5djTAD1cGYuMQK Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable > I think this is a limitation of driver may not be for HW. The right model= for > dma_chan is to be viewed as SW channels and not the ones of HW (yes that = is > how most of the drivers use that, but we can improve upon) >=20 > If we rework the driver to view dma_chan as SW channels, then you can acc= ept > multiple channel requests and accept based on if we are able link the cha= nnel to > that peripheral or not. In my understanding, the DMA driver does exactly that. However, it is not even loaded at the time the I2C driver wants a channel, so the dmaengine core defers the probe. That is the problem for optional DMA channels: we can't know when deferring probe won't help anymore and don't know when it is time to fall back to PIO. --YZ5djTAD1cGYuMQK Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJUiUm3AAoJEBQN5MwUoCm2ndkP+gPDbBbOcS/Hx5JDPz+xCH6L KGtMAMTX1nmoOyjedY1Igv1PdvAMyEn6/DQTP3RpeVW01QAfMIDBxXRKDngIIMwu ehrAlYoe0Z45vAjGMzCGUyJnx1y2EM8LRv0k2nymUw6224AFDOAASHDe25+Esxp1 qldeMa7HBfqt1HqX2SGoocgrlrERHG5cCz1HY4/C+qVkBtbLBfKnMDJtzvYk3leR sjEM/JVFXtGFOrXdte2rtg4qrmW/qvN1P+D+S7pA/xWO6AM2df/is0flp9utUjzG stnTn8U1RJRy8Wu+4aXAQcIPo+dCnMv98Z8a5Kk0t0fWpb0wOmkWrwZm3SgMhx6+ ULS9GSQckBC5JWAGR6FqDAqh1/Z9bZS6QtMUysVdixKHBqmKgQAqZimFGU2pmPjW 9ic5xQDfrO10sPnmNx6HLxaNsW/lwkoPjenC6rWqR3zUuhSuxwY8SL+81MlAhskC GaZ0Bq7PKbg0O0BSEzmdbKdY832yJaKqeO2/VN0LVeepmG0g08fC4W9/mFP6Nbig N9rjKsKh717+CaxA9npeQiR4qzrBMctbn0mi+XuTujxhwZxv/Mtr+ynFn8WMza63 cVXj77EmFqrcVIZKHJNX+ww51uJibJLb39XtWqQt+30AdzPAAGnQbMmuBkHEu5m3 N63vFokltQT9kp0/4t+s =wGbu -----END PGP SIGNATURE----- --YZ5djTAD1cGYuMQK--