From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Rosin Subject: prealloc_buffer_size and buffer_bytes_max Date: Thu, 21 May 2015 14:28:25 +0200 Message-ID: <555DCF69.9090008@lysator.liu.se> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail.lysator.liu.se (mail.lysator.liu.se [130.236.254.3]) by alsa0.perex.cz (Postfix) with ESMTP id 19C202612D1 for ; Thu, 21 May 2015 14:28:36 +0200 (CEST) List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: linux-arm-kernel@lists.infradead.org, alsa-devel@alsa-project.org, Alexandre Belloni List-Id: alsa-devel@alsa-project.org Hi! I got my hopes up when I read the commit message for c14e2591bf54 ASoC: atmel-pcm-dma: increase buffer_bytes_max. Quoting it: atmel-pcm-dma is not limited to a buffer size of 64kB like atmel-pcm-pdc. Increase buffer_bytes_max to 512kB to allow for higher bit rates (i.e. 32bps at 192kHz) to work correctly. By default, keep the prealloc at 64kB. However, as I (think I) request a bigger buffer it still caps out at 64kB. I'm using the latency argument of snd_pcm_set_params to control the buffer: snd_pcm_set_params(pcm, SND_PCM_FORMAT_S32_LE, SND_PCM_ACCESS_RW_INTERLEAVED, 2, /* channels */ 250000, /* rate */ 0, /* do not resample */ 90000); /* latency in us */ But snd_pcm_hw_params_get_buffer_size "only" returns 8192 frames (64kB) even if I request 9us * 250kHz * 2 * 4 = 180kB. If I change the prealloc from 64kB to 256kB I get a bigger buffer (and it works better too!). Admittedly I backported this patch on top of the linux-3.18-at91 branch from the Atmel git repo, so there might be some support missing that has gone in after 3.18? Or have I completely misunderstood, and these are unrelated buffers? Any insight in how I can get a big enough buffer without hacking the prealloc is appreciated! Cheers, Peter