From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.bootlin.com ([62.4.15.54]) by merlin.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gOeWL-0005Uq-Tz for linux-mtd@lists.infradead.org; Mon, 19 Nov 2018 08:03:03 +0000 Date: Mon, 19 Nov 2018 09:02:46 +0100 From: Boris Brezillon To: Naga Sureshkumar Relli Cc: "miquel.raynal@bootlin.com" , "richard@nod.at" , "dwmw2@infradead.org" , "computersforpeace@gmail.com" , "marek.vasut@gmail.com" , "linux-mtd@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "nagasuresh12@gmail.com" , "robh@kernel.org" , Michal Simek Subject: Re: [LINUX PATCH v12 3/3] mtd: rawnand: arasan: Add support for Arasan NAND Flash Controller Message-ID: <20181119090246.49060019@bbrezillon> In-Reply-To: References: <1541739641-17789-1-git-send-email-naga.sureshkumar.relli@xilinx.com> <1541739641-17789-4-git-send-email-naga.sureshkumar.relli@xilinx.com> <20181118204324.373ca9cc@bbrezillon> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 19 Nov 2018 06:20:28 +0000 Naga Sureshkumar Relli wrote: > H Boris, > > > -----Original Message----- > > From: Boris Brezillon [mailto:boris.brezillon@bootlin.com] > > Sent: Monday, November 19, 2018 1:13 AM > > To: Naga Sureshkumar Relli > > Cc: miquel.raynal@bootlin.com; richard@nod.at; dwmw2@infradead.org; > > computersforpeace@gmail.com; marek.vasut@gmail.com; linux-mtd@lists.infradead.org; linux- > > kernel@vger.kernel.org; nagasuresh12@gmail.com; robh@kernel.org; Michal Simek > > > > Subject: Re: [LINUX PATCH v12 3/3] mtd: rawnand: arasan: Add support for Arasan NAND > > Flash Controller > > > > On Thu, 15 Nov 2018 09:34:16 +0000 > > Naga Sureshkumar Relli wrote: > > > > > Hi Boris & Miquel, > > > > > > I am updating the driver by addressing your comments, and I have one > > > concern, especially in anfc_read_page_hwecc(), there I am checking for erased pages bit flips. > > > Since Arasan NAND controller doesn't have multibit error detection > > > beyond 24-bit( it can correct up to 24 bit), i.e. there is no indication from controller to detect > > uncorrectable error beyond 24bit. > > > > Do you mean that you can't detect uncorrectable errors, or just that it's not 100% sure to detect > > errors above max_strength? > Yes, in Arasan NAND controller there is no way to detect uncorrectable errors beyond 24-bit. So how do you detect uncorrectable errors when the strength is less than 24bits? > > > > > So I took some error count as default value(MULTI_BIT_ERR_CNT 16, I > > > put this based on the error count that I got while reading erased page on Micron device). > > > And during a page read, will just read the error count register and > > > compare this value with the default error count(16) and if it is more Than default then I am > > checking for erased page bit flips. > > > > Hm, that's wrong, especially if you set ecc_strength to something > 16. > Ok > > > > > I am doubting that this will not work in all cases. > > > > It definitely doesn't. > Ok > > > > > In my case it is just working because the error count that it got on an erased page is 16. > > > Could you please suggest a way to do detect erased_page bit flips when reading a page with > > HW-ECC?. > > > > I'm a bit lost. Is the problem only about bitflips in erase pages, or is it also impacting reads of > > written pages that lead to uncorrectable errors. > Yes, it is for both. But in case of read errors that we can't detect beyond 24-bit, then the answer from HW design team > Is that the flash part is bad. > Unfortunately till now we haven't ran into that situation(read errors of written pages beyond 24-bit). Can you please run nandbiterrs (availaible in mtd-utils). I fear your device won't pass the test. > But we are hitting this because of erased page reading(needed in case of ubifs). > > > > > Don't you have a bit (or several bits) reporting when the ECC engine was not able to correct > > data? I you do, you should base the "detect bitflips in erase pages" logic on this information. > Bit reporting for several bit errors is there only for Hamming(1bit correction and 2bit detection) but not in BCH. > Then I tend to agree with Miquel: your ECC engine is broken, and I'm not even sure how to deal with that yet.