From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Brown Subject: Re: [PATCH 1/2] powerpc: add platform registration for ALSA SoC drivers Date: Tue, 27 Apr 2010 22:11:18 +0100 Message-ID: <20100427211118.GD15083@opensource.wolfsonmicro.com> References: <1272314980-23679-1-git-send-email-timur@freescale.com> <1272350168.24542.6.camel@pasglop> <1272355624.3204.52.camel@odin> <4BD74D0C.40303@freescale.com> <20100427205924.GC15083@opensource.wolfsonmicro.com> <4BD7511F.7090201@freescale.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from opensource2.wolfsonmicro.com (opensource.wolfsonmicro.com [80.75.67.52]) by alsa0.perex.cz (Postfix) with ESMTP id 3EB0C24371 for ; Tue, 27 Apr 2010 23:11:19 +0200 (CEST) Content-Disposition: inline In-Reply-To: <4BD7511F.7090201@freescale.com> 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: Timur Tabi Cc: alsa-devel@alsa-project.org, Benjamin Herrenschmidt , kumar.gala@freescale.com, Grant Likely , linuxppc-dev@ozlabs.org, Liam Girdwood List-Id: alsa-devel@alsa-project.org On Tue, Apr 27, 2010 at 04:03:27PM -0500, Timur Tabi wrote: [Reflowing the text into 80 columns again] > Mark Brown wrote: > > It's entirely possible that if the board designer intended the verious > > SSIs to be used in concert they've done something like cross wire the > > clocks which creates a board-specific interrelationship that needs to be > > dealt with. > Fine, but I don't see how that can be handled with the current code. > Each SSI is independent, and audio is streamed to it via DMA. The > current SSI driver would need to be completely rewritten in order to > initiate both DMA operations simultaneously. The clocking is the least > of my problems. I believe the usual technique is to start the DMA then clock the bus - data doesn't flow over the bus until the clock appears and that appears everywhere simultaneously. Obviously some hardware really doesn't like having the DMA blocked like that, but not all. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from opensource2.wolfsonmicro.com (opensource.wolfsonmicro.com [80.75.67.52]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 42E8FB7D5C for ; Wed, 28 Apr 2010 07:11:21 +1000 (EST) Date: Tue, 27 Apr 2010 22:11:18 +0100 From: Mark Brown To: Timur Tabi Subject: Re: [alsa-devel] [PATCH 1/2] powerpc: add platform registration for ALSA SoC drivers Message-ID: <20100427211118.GD15083@opensource.wolfsonmicro.com> References: <1272314980-23679-1-git-send-email-timur@freescale.com> <1272350168.24542.6.camel@pasglop> <1272355624.3204.52.camel@odin> <4BD74D0C.40303@freescale.com> <20100427205924.GC15083@opensource.wolfsonmicro.com> <4BD7511F.7090201@freescale.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <4BD7511F.7090201@freescale.com> Cc: alsa-devel@alsa-project.org, kumar.gala@freescale.com, linuxppc-dev@ozlabs.org, Liam Girdwood List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Apr 27, 2010 at 04:03:27PM -0500, Timur Tabi wrote: [Reflowing the text into 80 columns again] > Mark Brown wrote: > > It's entirely possible that if the board designer intended the verious > > SSIs to be used in concert they've done something like cross wire the > > clocks which creates a board-specific interrelationship that needs to be > > dealt with. > Fine, but I don't see how that can be handled with the current code. > Each SSI is independent, and audio is streamed to it via DMA. The > current SSI driver would need to be completely rewritten in order to > initiate both DMA operations simultaneously. The clocking is the least > of my problems. I believe the usual technique is to start the DMA then clock the bus - data doesn't flow over the bus until the clock appears and that appears everywhere simultaneously. Obviously some hardware really doesn't like having the DMA blocked like that, but not all.