From mboxrd@z Thu Jan 1 00:00:00 1970 From: christian pellegrin Subject: Re: [PATCH 3/3] max3100: adds console support for MAX3100 Date: Mon, 22 Mar 2010 08:03:00 +0100 Message-ID: References: <1268987997-22746-1-git-send-email-chripell@fsfe.org> <20100322093157.705bf458@feng-i7> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100322093157.705bf458@feng-i7> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: spi-devel-general-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Feng Tang Cc: "greg-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org" , "david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org" , "linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org" , "akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org" , "alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org" List-Id: linux-serial@vger.kernel.org On Mon, Mar 22, 2010 at 2:31 AM, Feng Tang wrote: > > Hi Christian, Hi, > > You'd better not call max3110_sr (which calls spi_sync) here, a console's > putchar() func may be called in some atomic context. > ack, I didn't realize that. Unfortunately this makes reliable use of MAX3100 as a console near impossible. Some SPI master driver use workqueues (see the bit banging ones). I don't see any way to yield CPU to them while somehow wait the output has finished (a busy loop won't work: perhaps the thread calling the console has a higher priority than the one doing actual SPI output so the system will deadlock). The only way out I see is to provide a buffer large enough for all practical purposes. Will try it in the next version of the patch. Thanks. -- Christian Pellegrin, see http://www.evolware.org/chri/ "Real Programmers don't play tennis, or any other sport which requires you to change clothes. Mountain climbing is OK, and Real Programmers wear their climbing boots to work in case a mountain should suddenly spring up in the middle of the computer room." ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev