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 C752AEB8FD3 for ; Wed, 6 Sep 2023 13:47:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235272AbjIFNrc (ORCPT ); Wed, 6 Sep 2023 09:47:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58628 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237198AbjIFNrb (ORCPT ); Wed, 6 Sep 2023 09:47:31 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63F60E6B for ; Wed, 6 Sep 2023 06:47:26 -0700 (PDT) Received: from pendragon.ideasonboard.com (ftip006315900.acc1.colindale.21cn-nte.bt.net [81.134.214.249]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id BA32DDE2; Wed, 6 Sep 2023 15:45:57 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1694007957; bh=3M3fvvKZdlnyeobLySlvvCKUHqEgZInd3CnsocvLZ8Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tBujmTYr2rt7Bg3z2XLSbl1LsW0UnV7bsceVCebnpjihorFAJuTq/mO7YoRGK2KtJ 5oboUapVWoJHZTCScSh2ecJ5kx53Z+EaXvSkQPQmjQHPRakYEI9ch4YHb91VURX6/7 AFEPOrrwL4ZWdsLAOiBjfW9X++WzTdO1Vd+XaM1I= Date: Wed, 6 Sep 2023 16:47:37 +0300 From: Laurent Pinchart To: Sakari Ailus Cc: Jacopo Mondi , Hans Verkuil , linux-media@vger.kernel.org, tomi.valkeinen@ideasonboard.com, bingbu.cao@intel.com, hongju.wang@intel.com, Andrey Konovalov , Dmitry Perchanov , Naushir Patuck , David Plowman Subject: Re: [PATCH v3 07/10] media: uapi: Add generic 8-bit metadata format definitions Message-ID: <20230906134737.GA25420@pendragon.ideasonboard.com> References: <20230808075538.3043934-8-sakari.ailus@linux.intel.com> <9d3f512c-69c6-3789-83af-d151acd58ebe@xs4all.nl> <20230905164720.GC7971@pendragon.ideasonboard.com> <20230906123658.GF17308@pendragon.ideasonboard.com> <20230906133057.GN17308@pendragon.ideasonboard.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Wed, Sep 06, 2023 at 01:39:59PM +0000, Sakari Ailus wrote: > Hi Laurent, > > On Wed, Sep 06, 2023 at 04:30:57PM +0300, Laurent Pinchart wrote: > > On Wed, Sep 06, 2023 at 01:25:53PM +0000, Sakari Ailus wrote: > > > On Wed, Sep 06, 2023 at 03:36:58PM +0300, Laurent Pinchart wrote: > > > > On Wed, Sep 06, 2023 at 11:36:45AM +0000, Sakari Ailus wrote: > > > > > On Tue, Sep 05, 2023 at 07:47:20PM +0300, Laurent Pinchart wrote: > > > > > > On Fri, Aug 11, 2023 at 09:11:39AM +0000, Sakari Ailus wrote: > > > > > > > On Fri, Aug 11, 2023 at 08:31:16AM +0200, Jacopo Mondi wrote: > > > > > > > > > > +V4L2_META_FMT_GENERIC_CSI2_10 > > > > > > > > > > +----------------------------- > > > > > > > > > > + > > > > > > > > > > +V4L2_META_FMT_GENERIC_CSI2_10 contains packed 8-bit generic metadata, 10 bits > > > > > > > > > > +for each 8 bits of data. Every four bytes of metadata is followed by a single > > > > > > > > > > +byte of padding. The way the data is stored follows the CSI-2 specification. > > > > > > > > > > + > > > > > > > > > > +This format is also used on CSI-2 on 20 bits per sample format that packs two > > > > > > > > > > +bytes of metadata into one sample. > > > > > > > > > > + > > > > > > > > > > +This format is little endian. > > > > > > > > > > + > > > > > > > > > > +**Byte Order Of V4L2_META_FMT_GENERIC_CSI2_10.** > > > > > > > > > > +Each cell is one byte. "M" denotes a byte of metadata and "p" a byte of padding. > > > > > > > > > > > > > > > > > > I think you should document whether the padding is always 0 or can be any value. > > > > > > > > > Perhaps 'X' is a better 'name' for the padding byte in the latter case. > > > > > > > > > > > > > > > > Did I get this right that this format is supposed to work as the RAW10 > > > > > > > > CSI-2 packed image format, where 4 bytes contain the higher 8 bits of > > > > > > > > the 10 bits sample and the 5th byte every 4 contains the lower 2 bits of > > > > > > > > the previous 4 sample ? > > > > > > > > > > > > > > > > If that's the case, is 'padding' the correct term here ? > > > > > > > > > > > > > > What else would you call it? It'll be zeros that exist just due to the bit > > > > > > > depth used and as such not interesting at all. > > > > > > > > > > > > It's actually not 0, CCS requires the padding bytes to be 0x55. > > > > > > > > > > > > I wonder if the conformance test suite tests the contents of the padding > > > > > > bytes. > > > > > > > > > > I don't know. I could add the value is unspecified but as it has not been > > > > > specified, there's no change in meaning (just size). > > > > > > > > I started writing that I don't see how it could help applications to > > > > know that the padding byte is 0x55, but the SMIA++ embedded data parser > > > > in libcamera actually checks for it, and considers the embedded data to > > > > be erroneous if it has a different value. > > > > > > I think it's fine to check for it if you know it's CCS/SMIA++/SMIA embedded > > > data. But documenting it here isn't a great idea as then other uses of this > > > format definition would be excluded. > > > > I'm OK with that, but note that you've mentioned in a different patch in > > the same series that you wouldn't use the CCS media bus code for sensors > > that are compliant with the CCS packing and encoding but not the CCS > > register set. That's not very consistent :-) > > Which specific patch are you referring to? "[PATCH v3 09/10] media: Add media bus codes for MIPI CCS embedded data" You wrote "There are sensors that aren't fully compatible with CCS (including those compatible with SMIA and SMIA++) but I wouldn't expect the format to be used by devices that are entirely incompatible with CCS." -- Regards, Laurent Pinchart