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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 5F985C83000 for ; Thu, 30 Apr 2020 14:17:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3AB23206D9 for ; Thu, 30 Apr 2020 14:17:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="hF9DuKRe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726900AbgD3OR6 (ORCPT ); Thu, 30 Apr 2020 10:17:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58918 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726550AbgD3OR5 (ORCPT ); Thu, 30 Apr 2020 10:17:57 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 74F38C035494; Thu, 30 Apr 2020 07:17:57 -0700 (PDT) Received: from pendragon.ideasonboard.com (81-175-216-236.bb.dnainternet.fi [81.175.216.236]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id BCB9A321; Thu, 30 Apr 2020 16:17:54 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1588256274; bh=QnU3rVtRITdIUfU2XviScIgTzSx2RDZmgaWvifRzQj0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hF9DuKRecFqnhkjW16umg9StVJTv1XtdPj1bt7bJJH2hPVzD12H0CsirPrGfgg+2J XKN39xa14DmV4dGSwDDkucqmr0e60c6UjCmHLqMzSEslp/BAQrhkfWIkBmSXGd9ORk d7AoWSrG82eY5TGjNeeLk7KXp6Yj00JG8C15Vdq8= Date: Thu, 30 Apr 2020 17:17:53 +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: <20200430141753.GJ5856@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> <20200430135904.GI5856@pendragon.ideasonboard.com> <20200430141552.GO867@valkosipuli.retiisi.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200430141552.GO867@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 05:15:52PM +0300, Sakari Ailus wrote: > On Thu, Apr 30, 2020 at 04:59:04PM +0300, Laurent Pinchart wrote: > > 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). > > Sounds good to me. > > Jacopo's set exposing read-only subdevs completes the puzzle so the user > space should have all it needs, right? Until we run into the next missing piece :-) -- Regards, Laurent Pinchart