From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wi0-f176.google.com ([209.85.212.176]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1Wfnkx-0002u9-GO for linux-mtd@lists.infradead.org; Thu, 01 May 2014 09:58:20 +0000 Received: by mail-wi0-f176.google.com with SMTP id f8so407228wiw.15 for ; Thu, 01 May 2014 02:57:57 -0700 (PDT) From: Lee Jones To: linux-kernel@vger.kernel.org Subject: [PATCH 24/47] mtd: nand: stm_nand_bch: check erased page for zeros Date: Thu, 1 May 2014 10:56:31 +0100 Message-Id: <1398938214-17847-25-git-send-email-lee.jones@linaro.org> In-Reply-To: <1398938214-17847-1-git-send-email-lee.jones@linaro.org> References: <1398938214-17847-1-git-send-email-lee.jones@linaro.org> Cc: Lee Jones , computersforpeace@gmail.com, linux-mtd@lists.infradead.org, kernel@stlinux.com List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Detect an erased page, tolerating and correcting up to a specified number of bits at '0'. Downgrade uncorrectable ECC error for an erased page, tolerating 'sectors_per_page' bits at '0'. Signed-off-by: Lee Jones --- drivers/mtd/nand/stm_nand_bch.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/drivers/mtd/nand/stm_nand_bch.c b/drivers/mtd/nand/stm_nand_bch.c index 6d7ab79..2ff72c9 100644 --- a/drivers/mtd/nand/stm_nand_bch.c +++ b/drivers/mtd/nand/stm_nand_bch.c @@ -486,6 +486,33 @@ static uint8_t bch_erase_block(struct nandi_controller *nandi, } /* + * Detect an erased page, tolerating and correcting up to a specified number of + * bits at '0'. (For many devices, it is now deemed within spec for an erased + * page to include a number of bits at '0', either as a result of read-disturb + * behaviour or 'stuck-at-zero' failures.) Returns the number of corrected + * bits, or a '-1' if we have exceeded the maximum number of bits at '0' (likely + * to be a genuine uncorrectable ECC error). In the latter case, the data must + * be returned unmodified, in accordance with the MTD API. + */ +static int check_erased_page(uint8_t *data, uint32_t page_size, int max_zeros) +{ + uint8_t *b = data; + int zeros = 0; + int i; + + for (i = 0; i < page_size; i++) { + zeros += hweight8(~*b++); + if (zeros > max_zeros) + return -1; + } + + if (zeros) + memset(data, 0xff, page_size); + + return zeros; +} + +/* * Initialisation */ static int bch_check_compatibility(struct nandi_controller *nandi, -- 1.8.3.2