From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfram Sang Subject: Re: [PATCH] i2c: mxs: remove broken PIOQUEUE support Date: Thu, 1 Nov 2012 17:08:28 +0100 Message-ID: <20121101160828.GA18425@pengutronix.de> References: <1351771003-6071-1-git-send-email-w.sang@pengutronix.de> <201211011528.17596.marex@denx.de> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="9amGYk9869ThD9tj" Return-path: Content-Disposition: inline In-Reply-To: <201211011528.17596.marex-ynQEQJNshbs@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Marek Vasut Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Shawn Guo List-Id: linux-i2c@vger.kernel.org --9amGYk9869ThD9tj Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Nov 01, 2012 at 03:28:17PM +0100, Marek Vasut wrote: > Dear Wolfram Sang, >=20 > > This I2C master can do DMA and PIOQUEUE (PIO with FIFO). Originally, > > only PIOQEUE >=20 > PIOQUEUE ;-) Yup, right! >=20 > > was supported, then DMA support was added. The original > > intention was to keep PIOQUEUE since it has less overhead what is nice > > for small transfers. However, runtime switching between PIOQEUE and DMA > > depending on the transfer size never worked despite a lot of trying. > > Since PIOQUEUE mode itself was flaky (polling at places where interrupts > > failed to work) and the implementation also imposed a size limit for > > transfers, it is best to remove the support altogether which makes the > > driver a lot cleaner and more robust. If somebody really wants less > > overhead, plain PIO mode could still be implemented with the addidtional > > advantage that this mode is also available on MX23, too. >=20 > Yes, looks to be the way to go. >=20 > Reviewed-by: Marek Vasut Thanks. BTW have you tried combining all i2c-messages (msgs[]) of the transfer into one DMA chain? That would reduce overhead, too, no? Regards, Wolfram --=20 Pengutronix e.K. | Wolfram Sang | Industrial Linux Solutions | http://www.pengutronix.de/ | --9amGYk9869ThD9tj Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEARECAAYFAlCSnnwACgkQD27XaX1/VRtLWQCgxJaGhURLhp//cyL+33+6+xS/ QKgAoKmzp4RKpaMZt8fkUESoncsWHbQd =YFFv -----END PGP SIGNATURE----- --9amGYk9869ThD9tj--