From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5AA26C4167B for ; Mon, 4 Dec 2023 13:52:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344406AbjLDNwo convert rfc822-to-8bit (ORCPT ); Mon, 4 Dec 2023 08:52:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234455AbjLDNwc (ORCPT ); Mon, 4 Dec 2023 08:52:32 -0500 Received: from metis.whiteo.stw.pengutronix.de (metis.whiteo.stw.pengutronix.de [IPv6:2a0a:edc0:2:b01:1d::104]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BC051D2 for ; Mon, 4 Dec 2023 05:52:35 -0800 (PST) Received: from drehscheibe.grey.stw.pengutronix.de ([2a0a:edc0:0:c01:1d::a2]) by metis.whiteo.stw.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1rA9NB-0001MR-FQ; Mon, 04 Dec 2023 14:52:33 +0100 Received: from [2a0a:edc0:0:900:1d::4e] (helo=lupine) by drehscheibe.grey.stw.pengutronix.de with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1rA9NA-00DX4I-Py; Mon, 04 Dec 2023 14:52:32 +0100 Received: from pza by lupine with local (Exim 4.96) (envelope-from ) id 1rA9NA-000HGj-2K; Mon, 04 Dec 2023 14:52:32 +0100 Message-ID: Subject: Re: [PATCH v2 30/36] media: imx: Fix misuse of min_buffers_needed field From: Philipp Zabel To: Benjamin Gaignard , hverkuil@xs4all.nl, mchehab@kernel.org, tfiga@chromium.org, m.szyprowski@samsung.com, matt.ranostay@konsulko.com Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-staging@lists.linux.dev, kernel@collabora.com, Steve Longerbeam , Greg Kroah-Hartman , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team Date: Mon, 04 Dec 2023 14:52:32 +0100 In-Reply-To: <20231204132323.22811-31-benjamin.gaignard@collabora.com> References: <20231204132323.22811-1-benjamin.gaignard@collabora.com> <20231204132323.22811-31-benjamin.gaignard@collabora.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT User-Agent: Evolution 3.46.4-2 MIME-Version: 1.0 X-SA-Exim-Connect-IP: 2a0a:edc0:0:c01:1d::a2 X-SA-Exim-Mail-From: p.zabel@pengutronix.de X-SA-Exim-Scanned: No (on metis.whiteo.stw.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Benjamin, On Mo, 2023-12-04 at 14:23 +0100, Benjamin Gaignard wrote: > 'min_buffers_needed' is suppose to be used to indicate the number > of buffers needed by DMA engine to start streaming. > imx-media-capture driver doesn't use DMA engine and just want to specify > the minimum number of buffers to allocate when calling VIDIOC_REQBUFS. This is used by imx-media-csi and imx-ic-prpencvf. Both expect two buffers to setup the IDMAC DMA engine double buffer (see csi_idmac_setup_vb2_buf()/prp_setup_vb2_buf()). These functions can cope with less than two buffers queued, by using a special "underrun" buffer as a workaround, but the hardware does require two buffer addresses, so I'm not sure whether this really should be called a misuse of min_buffers_needed. regards Philipp