From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.bootlin.com ([62.4.15.54]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1fIUU4-00087o-4J for linux-mtd@lists.infradead.org; Tue, 15 May 2018 07:34:58 +0000 Date: Tue, 15 May 2018 09:34:29 +0200 From: Boris Brezillon To: Chris Moore Cc: "Wan, Jane (Nokia - US/Sunnyvale)" , "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" , "Bos, Ties \(Nokia - US/Sunnyvale\)" , "linux-mtd@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v7] mtd: rawnand: use bit-wise majority to recover the contents of ONFI parameter Message-ID: <20180515093429.34902670@bbrezillon> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 15 May 2018 06:45:51 +0200 Chris Moore wrote: > Hi, >=20 > Le 13/05/2018 =C3=A0 06:30, Wan, Jane (Nokia - US/Sunnyvale) a =C3=A9crit= =C2=A0: > > 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 th= e 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 > > =20 > > 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/na= nd_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(stru= ct nand_chip *chip, > > } > > =20 > > /* > > + * 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 =3D 0; i < bufsize; i++) { > > + u8 cnt, val; > > + > > + val =3D 0; > > + for (j =3D 0; j < 8; j++) { > > + cnt =3D 0; > > + for (k =3D 0; k < nsrcbufs; k++) { > > + const u8 *srcbuf =3D srcbufs[k]; > > + > > + if (srcbuf[i] & BIT(j)) > > + cnt++; > > + } > > + if (cnt > nsrcbufs / 2) > > + val |=3D BIT(j); > > + } > > + ((u8 *)dstbuf)[i] =3D val; > > + } > > +} > > + > > +/* > > * Check if the NAND chip is ONFI compliant, returns 1 if it is, 0 ot= herwise. > > */ > > static int nand_flash_detect_onfi(struct nand_chip *chip) > > @@ -5102,7 +5131,7 @@ static int nand_flash_detect_onfi(struct nand_chi= p *chip) > > return 0; > > =20 > > /* ONFI chip: allocate a buffer to hold its parameter page */ > > - p =3D kzalloc(sizeof(*p), GFP_KERNEL); > > + p =3D kzalloc((sizeof(*p) * 3), GFP_KERNEL); > > if (!p) > > return -ENOMEM; > > =20 > > @@ -5113,21 +5142,32 @@ static int nand_flash_detect_onfi(struct nand_c= hip *chip) > > } > > =20 > > for (i =3D 0; i < 3; i++) { > > - ret =3D nand_read_data_op(chip, p, sizeof(*p), true); > > + ret =3D nand_read_data_op(chip, &p[i], sizeof(*p), true); > > if (ret) { > > ret =3D 0; > > goto free_onfi_param_page; > > } > > =20 > > - if (onfi_crc16(ONFI_CRC_BASE, (uint8_t *)p, 254) =3D=3D > > + if (onfi_crc16(ONFI_CRC_BASE, (u8 *)&p[i], 254) =3D=3D > > le16_to_cpu(p->crc)) { > > + if (i) > > + memcpy(p, &p[i], sizeof(*p)); > > break; > > } > > } > > =20 > > if (i =3D=3D 3) { > > - pr_err("Could not find valid ONFI parameter page; aborting\n"); > > - goto free_onfi_param_page; > > + const void *srcbufs[3] =3D {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) !=3D > > + le16_to_cpu(p->crc)) { > > + pr_err("ONFI parameter recovery failed, aborting\n"); > > + goto free_onfi_param_page; > > + } > > } > > =20 > > /* Check version */ =20 >=20 > 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=20 > I repeat below? Because I want the nand_bit_wise_majority() function to work with nsrcbufs > 3 (the ONFI spec says there's at least 3 copy of the param page, but NAND vendor can decide to put more). Also, if the X copies of the PARAM are corrupted (which is rather unlikely), that means we already spent quite a lot of time reading the different copies and calculating the CRC, so I think we don't care about perf optimizations when doing bit-wise majority. >=20 > The three sample bitwise majority can be implemented without bit level=20 > manipulation using the identity: > majority3(a, b, c) =3D (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=20 > a time depending on the hardware. >=20 > This method is not only faster and but also more compact. >=20 > Cheers, > Chris >=20 >=20 > ______________________________________________________ > Linux MTD discussion mailing list > http://lists.infradead.org/mailman/listinfo/linux-mtd/