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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: xilinx.com X-MS-Exchange-CrossTenant-Network-Message-Id: 66874921-7621-4c92-6c93-08d64eb6164e X-MS-Exchange-CrossTenant-originalarrivaltime: 20 Nov 2018 07:02:08.3194 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 657af505-d5df-48d0-8300-c31994686c5c X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN6PR02MB2403 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Boris, > -----Original Message----- > From: Boris Brezillon [mailto:boris.brezillon@bootlin.com] > Sent: Monday, November 19, 2018 1:33 PM > 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.infra= dead.org; linux- > kernel@vger.kernel.org; nagasuresh12@gmail.com; robh@kernel.org; Michal S= imek > > Subject: Re: [LINUX PATCH v12 3/3] mtd: rawnand: arasan: Add support for = Arasan NAND > Flash Controller >=20 > On Mon, 19 Nov 2018 06:20:28 +0000 > Naga Sureshkumar Relli wrote: >=20 > > 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 chec= king 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. >=20 > So how do you detect uncorrectable errors when the strength is less than > 24bits? Below or equal to the level of ECC strength, controller will definitely cor= rect.=20 But beyond the level of ECC strength, it won't even detect the errors. >=20 > > > > > > > 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 p= age 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 mo= re Than default then I > am > > > checking for erased page bit flips. > > > > > > Hm, that's wrong, especially if you set ecc_strength to something > 1= 6. > > 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 o= n an erased page is 16. > > > > Could you please suggest a way to do detect erased_page bit flips w= hen 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 be= yond 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 o= f written pages beyond > 24-bit). >=20 > Can you please run nandbiterrs (availaible in mtd-utils). I fear your > device won't pass the test. Yes, nandbiterror test is passing till 24bit, after that it is failing. >=20 > > But we are hitting this because of erased page reading(needed in case o= f 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 cor= rection and 2bit > detection) but not in BCH. > > >=20 > Then I tend to agree with Miquel: your ECC engine is broken, and I'm > not even sure how to deal with that yet. So as per the Miquel's suggestion, can I proceed to add the below one? "you should re-read the page in raw mode and check for the number of bitfli= ps manually (thanks to the helpers in the core). Again, if the number of BF= is above 16, we can assume the page is bad and increment ->ecc.failed acco= rdingly." Thanks, Naga Sureshkumar Relli