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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 93537C4724C for ; Thu, 30 Apr 2020 13:59:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 742692076D for ; Thu, 30 Apr 2020 13:59:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="m0nCqzOK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726975AbgD3N7N (ORCPT ); Thu, 30 Apr 2020 09:59:13 -0400 Received: from perceval.ideasonboard.com ([213.167.242.64]:37628 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729166AbgD3N7J (ORCPT ); Thu, 30 Apr 2020 09:59:09 -0400 Received: from pendragon.ideasonboard.com (81-175-216-236.bb.dnainternet.fi [81.175.216.236]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id E6246321; Thu, 30 Apr 2020 15:59:05 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1588255146; bh=GhmU8YETMOVIz97f3awqWGN1baPnypD27desAmZxvnM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=m0nCqzOK1A1eW641+wJC9vh12s4/oo687inR7KwWAJ0KfqiiA33qRsLDxYcMx6ii6 nLBqmMij+oZZhbjtiWkUkW2pvzh+f/SZwuwlfKT6O9T4OqGBt/h223EPPZfeexVlUe 6Cgq6VmXqw2elz+zFvEkTwg+mGUak8lKvy5fWD4o= Date: Thu, 30 Apr 2020 16:59:04 +0300 From: Laurent Pinchart To: Sakari Ailus Cc: Daniel Gomez , mchehab@kernel.org, hverkuil-cisco@xs4all.nl, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 1/3] media: v4l2-subdev.h: Add min and max enum Message-ID: <20200430135904.GI5856@pendragon.ideasonboard.com> References: <20200414200151.80089-1-daniel@qtec.com> <20200414200151.80089-2-daniel@qtec.com> <20200430094233.GE867@valkosipuli.retiisi.org.uk> <20200430111014.GD5856@pendragon.ideasonboard.com> <20200430133125.GL867@valkosipuli.retiisi.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200430133125.GL867@valkosipuli.retiisi.org.uk> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sakari, On Thu, Apr 30, 2020 at 04:31:25PM +0300, Sakari Ailus wrote: > On Thu, Apr 30, 2020 at 02:10:14PM +0300, Laurent Pinchart wrote: > > On Thu, Apr 30, 2020 at 12:42:33PM +0300, Sakari Ailus wrote: > >> On Tue, Apr 14, 2020 at 10:01:49PM +0200, Daniel Gomez wrote: > >>> Add min and max structures to the v4l2-subdev callback in order to allow > >>> the subdev to return a range of valid frame intervals. > >>> > >>> This would operate similar to the struct v4l2_subdev_frame_size_enum and > >>> its max and min values for the width and the height. In this case, the > >>> possibility to return a frame interval range is added to the v4l2-subdev level > >>> whenever the v4l2 device operates in step-wise or continuous mode. > >> > >> The current API only allows providing a list of enumerated values. That is > >> limiting indeed, especially on register list based sensor drivers where > >> vertical blanking is configurable. > >> > >> I guess this could be extended to cover what V4L2, more or less. If we tell > >> it's a range, is it assumed to be contiguous? We don't have try operation > >> for the frame interval, but I guess set is good enough. The fraction is > >> probably best for TV standards but it's not what camera sensors natively > >> use. (But for a register list based driver, the established practice > >> remains to use frame interval.) > >> > >> I'm also wondering the effect on existing user space; if a driver gives a > >> range, how will the existing programs work with such a driver? > >> > >> I'd add an anonymous union with the interval field, the other field being > >> min_interval. Then the current applications would get the minimum interval > >> and still continue to function. I guess compilers are modern enough these > >> days we can have an anonymous union in the uAPI? > > > > We can discuss all this, but given patch 3/3 in this series, I think > > this isn't the right API :-) The sensor driver should not expose the > > frame interval enumeration API. It should instead expose control of the > > frame rate through V4L2_CID_PIXEL_RATE, V4L2_CID_HBLANK and > > V4L2_CID_VBLANK. > > > > That would require also exposing the size of the pixel array (and the > analogue crop), in order to provide all the necessary information to > calculate the frame rate. No objections there; this is a new driver. > > There are however existing drivers that implement s_frame_interval subdev > ioctl; those might benefit from this one. Or would you implement the pixel > rate based control as well, and effectively deprecate the s_frame_interval > on those? That's what I would recommend, yes. I would only keep .s_frame_interval() for sensors that expose that concept at the hardware level (for instance with an integrated ISP whose firmware exposes a frame interval or frame rate control). > >>> Signed-off-by: Daniel Gomez > >>> --- > >>> include/uapi/linux/v4l2-subdev.h | 6 +++++- > >>> 1 file changed, 5 insertions(+), 1 deletion(-) > >>> > >>> diff --git a/include/uapi/linux/v4l2-subdev.h b/include/uapi/linux/v4l2-subdev.h > >>> index 03970ce30741..ee15393c58cd 100644 > >>> --- a/include/uapi/linux/v4l2-subdev.h > >>> +++ b/include/uapi/linux/v4l2-subdev.h > >>> @@ -117,6 +117,8 @@ struct v4l2_subdev_frame_interval { > >>> * @code: format code (MEDIA_BUS_FMT_ definitions) > >>> * @width: frame width in pixels > >>> * @height: frame height in pixels > >>> + * @min_interval: min frame interval in seconds > >>> + * @max_interval: max frame interval in seconds > >>> * @interval: frame interval in seconds > >>> * @which: format type (from enum v4l2_subdev_format_whence) > >>> */ > >>> @@ -126,9 +128,11 @@ struct v4l2_subdev_frame_interval_enum { > >>> __u32 code; > >>> __u32 width; > >>> __u32 height; > >>> + struct v4l2_fract min_interval; > >>> + struct v4l2_fract max_interval; > >> > >> This changes the memory layout of the struct and breaks the ABI. Any new > >> fields in the struct may only replace reserved fields while the rest must > >> stay unchanged. > >> > >>> struct v4l2_fract interval; > >>> __u32 which; > >>> - __u32 reserved[8]; > >>> + __u32 reserved[4]; > >>> }; > >>> > >>> /** -- Regards, Laurent Pinchart