From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pidgin.makrotopia.org (pidgin.makrotopia.org [185.142.180.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E97C1286AF; Thu, 18 Apr 2024 22:52:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.142.180.65 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713480770; cv=none; b=lsV2BjQrMUSqcZaXbGrlyaGSWb6QTUhEZzT8kLYG0ihz9MWiUrsDePGT0mJu+CCYMGRnBS5CmvvdXZJezP157c6jgVyR1q0uiYzFOGXvmg9qaDA3XsRRgYbK4ADhIWNlLMEGO83MjaCVhn5dSoKRwAQlacb9hjkfUVQncVXAVkA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713480770; c=relaxed/simple; bh=e9cfJN8rNWU9caYstywKsUUR/GDFScyvCazNhCJrrfM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DJKPagMNalECQMf7/jSH/lsHSIheoSKhc7bd4GCjYiKNOVuehlnO/AV7eOHFtP93jBq+BTSCEGYnEYzzTPX3MHIW3kGTz78zxuvQzfGFzidLnSTLJCQi3cDBKA5MKn/cbaxJHwaSWKetc48ofIG8J/9Xm85h71Wo2G8n3f5jQqc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=makrotopia.org; spf=pass smtp.mailfrom=makrotopia.org; arc=none smtp.client-ip=185.142.180.65 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=makrotopia.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=makrotopia.org Received: from local by pidgin.makrotopia.org with esmtpsa (TLS1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.96.2) (envelope-from ) id 1rxabl-00033c-35; Thu, 18 Apr 2024 22:51:58 +0000 Date: Thu, 18 Apr 2024 23:51:49 +0100 From: Daniel Golle To: Bart Van Assche Cc: Rob Herring , Krzysztof Kozlowski , Conor Dooley , Ulf Hansson , Jens Axboe , Dave Chinner , Jan Kara , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Damien Le Moal , Li Lingfeng , Christian Brauner , Christian Heusel , Min Li , Adrian Hunter , Avri Altman , Hannes Reinecke , Christian Loehle , Bean Huo , Yeqi Fu , Victor Shih , Christophe JAILLET , Dominique Martinet , "Ricardo B. Marliere" , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mmc@vger.kernel.org, linux-block@vger.kernel.org Subject: Re: [PATCH 3/8] block: add new genhd flag GENHD_FL_NVMEM Message-ID: References: <89abd9ab93783da0e8934ebc03d66559f78f6060.1711048433.git.daniel@makrotopia.org> <7027ccdc-878a-420e-a7ea-5156e1d67b8a@acm.org> <192acb8f-47b8-426c-bcc9-ef214a797f26@acm.org> Precedence: bulk X-Mailing-List: linux-mmc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <192acb8f-47b8-426c-bcc9-ef214a797f26@acm.org> On Fri, Mar 22, 2024 at 12:22:32PM -0700, Bart Van Assche wrote: > On 3/22/24 11:07, Daniel Golle wrote: > > On Fri, Mar 22, 2024 at 10:49:48AM -0700, Bart Van Assche wrote: > > > On 3/21/24 12:33, Daniel Golle wrote: > > > > enum { > > > > GENHD_FL_REMOVABLE = 1 << 0, > > > > GENHD_FL_HIDDEN = 1 << 1, > > > > GENHD_FL_NO_PART = 1 << 2, > > > > + GENHD_FL_NVMEM = 1 << 3, > > > > }; > > > > > > What would break if this flag wouldn't exist? > > > > As both, MTD and UBI already act as NVMEM providers themselves, once > > the user creates a ubiblock device or got CONFIG_MTD_BLOCK=y set in their > > kernel configuration, we would run into problems because both, the block > > layer as well as MTD or UBI would try to be an NVMEM provider for the same > > device tree node. > > Why would both MTD and UBI try to be an NVMEM provider for the same > device tree node? I didn't mean that both MTD and UBI would **simultanously** try to act as NVMEM providers for the same device tree node. What I meant was that either of them can act as an NVMEM provider while at the same time also providing an emulated block device (mtdblock xor ubiblock). Hence those emulated block devices will have to be excluded from acting as NVMEM providers. In this patch I suggest to do this by opt-in of block drivers which should potentially provide NVMEM (typically mmcblk). I apologize for the confusion and assume that wasn't clear from the wording I've used. I hope it's more clear now. Alternatively it could also be solved via opt-out of ubiblock and mtdblock devices using the inverted flag (GENHD_FL_NO_NVMEM) -- however, this has previously been criticized and I was asked to rather make it opt-in.[1] > Why can't this patch series be implemented such that > a partition UUID occurs in the device tree and such that other code > scans for that partition UUID? This is actually one way this very series allows one to handle this: by identifying a partition using its partuuid. However, it's also quite common that the MMC boot **hardware** partitions are used to store MAC addresses and/or Wi-Fi calibration data. In this case there is no partition table and the NVMEM provider has to act directly on the whole disk device (which is only a few megabytes in size in case of those mmcblkXbootY devices and never has a partition table). [1]: https://patchwork.kernel.org/comment/25432948/