Re: [PATCH v2] mtd: rawnand: xway: No hardcoded ECC engine, use device tree setting
From: Miquel Raynal
Date: Mon Sep 27 2021 - 12:31:57 EST
Sorry for the delay, I had to rethink about the problem first.
jan@xxxxxx wrote on Sat, 18 Sep 2021 23:26:48 +0200:
> Hi Miquèl,
> > Yes this was my understanding, that only software ECC engine was
> > supported. The mainline driver shows absolutely no signs of hardware
> > ECC engine support.
> > Perhaps however you mean that on-die ECC engine are not supported
> > anymore because of the engine_type being set in attach_chip()?
> Yes, this is exactly the issue.
> > If yes then indeed there is something to do, perhaps checking if an
> > engine has been already set is enough? You can try something like:
> > if (engine_type == unknown)
> > engine_type = soft;
> Checking for NAND_ECC_ENGINE_TYPE_INVALID doesn't work, as the engine
> type is already set to NAND_ECC_ENGINE_TYPE_ON_HOST by rawnand_dt_init.
> The code there seems to expect that chip->ecc.engine_type contains the
> default value, which is no longer the case after commit 525914b5bd8
> ("mtd: rawnand: xway: Move the ECC initialization to ->attach_chip()").
This is indeed an issue and should be fixed. However the solution is I
think already available in the raw NAND core (but I had to dig into the
code again to remember how I wanted to handle this).
> The following in attach_chip works:
> if (chip->ecc.engine_type == NAND_ECC_ENGINE_TYPE_ON_HOST)
> chip->ecc.engine_type = NAND_ECC_ENGINE_TYPE_SOFT;
If you look at the rawnand_dt_init() function  the logic is:
Is the user configuration (DT) valid ? if yes take it.
Is the NAND controller driver setting a default mode? if yes take it.
Otherwise take the raw NAND subsystem default: ON_HOST.
This logic happens very soon in the init process so the default mode
for the driver should be provided before the nand_scan() call.
So what I propose is:
- in the driver probe: set the default to software ECC
- in the attach() hook: drop the line setting the engine_type to SOFT.
Please check the below diff and tell me if it works for you. I'll then
propose a wider series fixing the other drivers as well.
> However, this will also silently use the software ECC engine if anyone
> actually configures the on-host hardware ECC engine in the device tree
> (which is of course unsupported for xway).
diff --git a/drivers/mtd/nand/raw/xway_nand.c b/drivers/mtd/nand/raw/xway_nand.c
index 26751976e502..d9e167dbb717 100644
@@ -148,9 +148,8 @@ static void xway_write_buf(struct nand_chip *chip, const u_char *buf, int len)
static int xway_attach_chip(struct nand_chip *chip)
- chip->ecc.engine_type = NAND_ECC_ENGINE_TYPE_SOFT;
- if (chip->ecc.algo == NAND_ECC_ALGO_UNKNOWN)
+ if (chip->ecc.engine_type == NAND_ECC_ENGINE_TYPE_SOFT &&
+ chip->ecc.algo == NAND_ECC_ALGO_UNKNOWN)
chip->ecc.algo = NAND_ECC_ALGO_HAMMING;
@@ -219,6 +218,14 @@ static int xway_nand_probe(struct platform_device *pdev)
| NAND_CON_SE_P | NAND_CON_WP_P | NAND_CON_PRE_P
| cs_flag, EBU_NAND_CON);
+ * This controller has no hardware ECC engine and the driver assumes
+ * that the default ECC engine should be TYPE_SOFT. Set ->engine_type
+ * before the NAND registration in order to provide a default value.
+ data->chip.ecc.engine_type = NAND_ECC_ENGINE_TYPE_SOFT;
/* Scan to find existence of the device */
err = nand_scan(&data->chip, 1);