H Boris, > -----Original Message----- > From: Boris Brezillon [mailto:boris.brezil...@bootlin.com] > Sent: Monday, November 19, 2018 1:13 AM > To: Naga Sureshkumar Relli <nagas...@xilinx.com> > Cc: miquel.ray...@bootlin.com; rich...@nod.at; dw...@infradead.org; > computersforpe...@gmail.com; marek.va...@gmail.com; > linux-...@lists.infradead.org; linux- > ker...@vger.kernel.org; nagasures...@gmail.com; r...@kernel.org; Michal Simek > <mich...@xilinx.com> > 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 <nagas...@xilinx.com> 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 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). 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. Thanks, Naga Sureshkumar Relli
