From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from skprod2.natinst.com ([130.164.80.23] helo=ni.com) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1YkyTV-0001y3-Fp for linux-mtd@lists.infradead.org; Wed, 22 Apr 2015 17:30:14 +0000 Date: Wed, 22 Apr 2015 12:29:44 -0500 From: Ben Shelton To: dwmw2@infradead.org, computersforpeace@gmail.com, dedekind1@gmail.com, adrian.hunter@intel.com, linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Adding subpage support to NAND driver -- backwards compatibility concerns Message-ID: <20150422172944.GA4134@bshelton-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Cc: punnaiah.choudary.kalluri@xilinx.com, xander.huff@ni.com, joshc@ni.com List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi all, We're currently carrying a patch out of tree to add subpage read and write support to the pl353_nand driver. Xilinx is currently working to mainline this driver; see http://www.spinics.net/lists/devicetree/msg76307.html We'd like to upstream our patch, but my concern is that UBIFS behaves differently when it knows that the flash device supports subpages. I have a couple of questions related to that: - I know from experience that bad things happen when you use a kernel without subpage support with an UBIFS filesystem that was formatted with subpage support. Is it safe to do the opposite (kernel with subpage support / UBIFS filesystem formatted without subpage support)? - Assuming that it isn't safe, what's the best way to add subpage support to this driver in an upstreamable way / without breaking people? Would it be sufficient to add subpage support as a Kconfig option that's disabled by default with a strongly-worded message describing the consequences of enabling it? Thanks, Ben