From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752222AbeEOEqC (ORCPT ); Tue, 15 May 2018 00:46:02 -0400 Received: from smtp4-g21.free.fr ([212.27.42.4]:44290 "EHLO smtp4-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750877AbeEOEqA (ORCPT ); Tue, 15 May 2018 00:46:00 -0400 Subject: Re: [PATCH v7] mtd: rawnand: use bit-wise majority to recover the contents of ONFI parameter To: "Wan, Jane (Nokia - US/Sunnyvale)" , "Boris.Brezillon@bootlin.com" , "miquel.raynal@bootlin.com" , "dwmw2@infradead.org" , "computersforpeace@gmail.com" , "richard@nod.at" , "marek.vasut@gmail.com" , "yamada.masahiro@socionext.com" , "prabhakar.kushwaha@nxp.com" , "shawnguo@kernel.org" , "jagdish.gediya@nxp.com" , "shreeya.patel23498@gmail.com" Cc: "Bos, Ties (Nokia - US/Sunnyvale)" , "linux-mtd@lists.infradead.org" , "linux-kernel@vger.kernel.org" References: From: Chris Moore Message-ID: Date: Tue, 15 May 2018 06:45:51 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Le 13/05/2018 à 06:30, Wan, Jane (Nokia - US/Sunnyvale) a écrit : > Per ONFI specification (Rev. 4.0), if all parameter pages have invalid CRC values, the bit-wise majority may be used to recover the contents of the parameter pages from the parameter page copies present. > > Signed-off-by: Jane Wan > --- > v7: change debug print messages > v6: support the cases that srcbufs are not contiguous > v5: make the bit-wise majority functon generic > v4: move the bit-wise majority code in a separate function > v3: fix warning message detected by kbuild test robot > v2: rebase the changes on top of v4.17-rc1 > > drivers/mtd/nand/raw/nand_base.c | 50 ++++++++++++++++++++++++++++++++++---- > 1 file changed, 45 insertions(+), 5 deletions(-) > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c > index 72f3a89..b43b784 100644 > --- a/drivers/mtd/nand/raw/nand_base.c > +++ b/drivers/mtd/nand/raw/nand_base.c > @@ -5087,6 +5087,35 @@ static int nand_flash_detect_ext_param_page(struct nand_chip *chip, > } > > /* > + * Recover data with bit-wise majority > + */ > +static void nand_bit_wise_majority(const void **srcbufs, > + unsigned int nsrcbufs, > + void *dstbuf, > + unsigned int bufsize) > +{ > + int i, j, k; > + > + for (i = 0; i < bufsize; i++) { > + u8 cnt, val; > + > + val = 0; > + for (j = 0; j < 8; j++) { > + cnt = 0; > + for (k = 0; k < nsrcbufs; k++) { > + const u8 *srcbuf = srcbufs[k]; > + > + if (srcbuf[i] & BIT(j)) > + cnt++; > + } > + if (cnt > nsrcbufs / 2) > + val |= BIT(j); > + } > + ((u8 *)dstbuf)[i] = val; > + } > +} > + > +/* > * Check if the NAND chip is ONFI compliant, returns 1 if it is, 0 otherwise. > */ > static int nand_flash_detect_onfi(struct nand_chip *chip) > @@ -5102,7 +5131,7 @@ static int nand_flash_detect_onfi(struct nand_chip *chip) > return 0; > > /* ONFI chip: allocate a buffer to hold its parameter page */ > - p = kzalloc(sizeof(*p), GFP_KERNEL); > + p = kzalloc((sizeof(*p) * 3), GFP_KERNEL); > if (!p) > return -ENOMEM; > > @@ -5113,21 +5142,32 @@ static int nand_flash_detect_onfi(struct nand_chip *chip) > } > > for (i = 0; i < 3; i++) { > - ret = nand_read_data_op(chip, p, sizeof(*p), true); > + ret = nand_read_data_op(chip, &p[i], sizeof(*p), true); > if (ret) { > ret = 0; > goto free_onfi_param_page; > } > > - if (onfi_crc16(ONFI_CRC_BASE, (uint8_t *)p, 254) == > + if (onfi_crc16(ONFI_CRC_BASE, (u8 *)&p[i], 254) == > le16_to_cpu(p->crc)) { > + if (i) > + memcpy(p, &p[i], sizeof(*p)); > break; > } > } > > if (i == 3) { > - pr_err("Could not find valid ONFI parameter page; aborting\n"); > - goto free_onfi_param_page; > + const void *srcbufs[3] = {p, p + 1, p + 2}; > + > + pr_warn("Could not find a valid ONFI parameter page, trying bit-wise majority to recover it\n"); > + nand_bit_wise_majority(srcbufs, ARRAY_SIZE(srcbufs), p, > + sizeof(*p)); > + > + if (onfi_crc16(ONFI_CRC_BASE, (u8 *)p, 254) != > + le16_to_cpu(p->crc)) { > + pr_err("ONFI parameter recovery failed, aborting\n"); > + goto free_onfi_param_page; > + } > } > > /* Check version */ This version is still hard coded for a three sample bitwise majority vote. So why not use the method which I suggested previously for v2 and which I repeat below? The three sample bitwise majority can be implemented without bit level manipulation using the identity: majority3(a, b, c) = (a & b) | (a & c) | (b & c) This can be factorized slightly to (a & (b | c)) | (b & c) This enables the operation to be performed 8, 16, 32 or even 64 bits at a time depending on the hardware. This method is not only faster and but also more compact. Cheers, Chris