mtd: nand: Warn the user if the selected ECC strength is too weak

This commit makes use of the chip->ecc_strength_ds and chip->ecc_step_ds which
contain the datasheet minimum requested ECC strength to produce a noisy warning
if the configured ECC strength is weaker.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 0c1593be69e3ce7affb0986c5ece774252a7873f..41167e9e991e4e50c1e1c2b72dbc468d654db22d 100644 (file)
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -3794,6 +3794,39 @@ int nand_scan_ident(struct mtd_info *mtd, int maxchips,
 }
 EXPORT_SYMBOL(nand_scan_ident);
 
+/*
+ * Check if the chip configuration meet the datasheet requirements.
+
+ * If our configuration corrects A bits per B bytes and the minimum
+ * required correction level is X bits per Y bytes, then we must ensure
+ * both of the following are true:
+ *
+ * (1) A / B >= X / Y
+ * (2) A >= X
+ *
+ * Requirement (1) ensures we can correct for the required bitflip density.
+ * Requirement (2) ensures we can correct even when all bitflips are clumped
+ * in the same sector.
+ */
+static bool nand_ecc_strength_good(struct mtd_info *mtd)
+{
+       struct nand_chip *chip = mtd->priv;
+       struct nand_ecc_ctrl *ecc = &chip->ecc;
+       int corr, ds_corr;
+
+       if (ecc->size == 0 || chip->ecc_step_ds == 0)
+               /* Not enough information */
+               return true;
+
+       /*
+        * We get the number of corrected bits per page to compare
+        * the correction density.
+        */
+       corr = (mtd->writesize * ecc->strength) / ecc->size;
+       ds_corr = (mtd->writesize * chip->ecc_strength_ds) / chip->ecc_step_ds;
+
+       return corr >= ds_corr && ecc->strength >= chip->ecc_strength_ds;
+}
 
 /**
  * nand_scan_tail - [NAND Interface] Scan for the NAND device
@@ -4014,6 +4047,9 @@ int nand_scan_tail(struct mtd_info *mtd)
                ecc->layout->oobavail += ecc->layout->oobfree[i].length;
        mtd->oobavail = ecc->layout->oobavail;
 
+       /* ECC sanity check: warn noisily if it's too weak */
+       WARN_ON(!nand_ecc_strength_good(mtd));
+
        /*
         * Set the number of read / write steps for one page depending on ECC
         * mode.