From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans-Christian Egtvedt Subject: Re: Can DMA address, periods, buffer size, etc change after hw_params is called? Date: Thu, 29 Jan 2009 11:10:34 +0100 Message-ID: <20090129111034.632c5dcf@hcegtvedt> References: <20090129081825.241be9e4@hcegtvedt> <498164BC.6080907@ladisch.de> <20090129094332.2728c908@hcegtvedt> <49816FA2.3030108@ladisch.de> <20090129103554.4a02cb04@hcegtvedt> <49817E17.8040401@ladisch.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from relay.atmel.no (relay.atmel.no [80.232.32.139]) by alsa0.perex.cz (Postfix) with ESMTP id 5BAF8103869 for ; Thu, 29 Jan 2009 11:10:37 +0100 (CET) In-Reply-To: <49817E17.8040401@ladisch.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: Clemens Ladisch Cc: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org On Thu, 29 Jan 2009 10:59:51 +0100 Clemens Ladisch wrote: > Hans-Christian Egtvedt wrote: > > Okay, so to be sure I setup and release my cyclic DMA buffer safely > > I could use the following model: > > > > in prepare callback setup the DMA buffer, once when called. The > > hardware parameters should not change at this point. > > > > If I get a hw_params callback after a prepare, then release the DMA > > buffer, and set it up again in the prepare callback? > > > > Final cleanup of the DMA buffer can/should be done in hw_free? > > This would work, but doing it in the hw_params callback would be a > little more simple: > * In hw_params, free the old buffer (if it exists), then setup the > buffer; I think I was not 100% clear, in addition to call snd_pcm_lib_malloc_pages() in hw_params, I also need to hand over the DMA buffer information to a prepare function in the DMA driver I use with this sound hardware. So I follow the scheme for free/setup of buffers for my DMA controller setup as well. hw_params, release DMA controller if exists, then prepare DMA controller. > * in hw_free, free the buffer. > Which I do by calling snd_pcm_lib_free_pages(). and then in hw_free, release DMA controller if exists. > As a rule of thumb, the callbacks open/close, hw_params/hw_free and > start/stop trigger are mostly symmetrical, and any resources should be > allocated and freed in the functions that belong together. (The start > trigger is a special case because it uses two callbacks, prepare and > trigger with TRIGGER_START.) > > The hw_params and prepare callbacks can be called multiple times. > Noted, which means I should reprepare my DMA controller as well every time I get a hw_params callback and do snd_pcm_lib_malloc_pages(). > > Is there a flow chart which shows how the different callbacks can be > > called? > > Not yet. > Would probably help me a lot to see the actual flow of the callbacks. -- Best regards, Hans-Christian Egtvedt