[PATCH 0/2] mtd: rawnand: denali: clean-up unnecessary hook and device reset

[PATCH 0/2] mtd: rawnand: denali: clean-up unnecessary hook and device reset

[Masahiro Yamada]

As I replied to Boris [1],
I took a closer look for further cleanups.
I test this series on my board.

Remove mis-implemented ->dev_ready hook.
Remove unnecessary device resetting because
nand_scan_ident() reset devices anyway.

[1] http://patchwork.ozlabs.org/patch/960160/



Masahiro Yamada (2):
  mtd: rawnand: denali: remove ->dev_ready() hook
  mtd: rawnand: denali: remove denali_reset_banks()

 drivers/mtd/nand/raw/denali.c | 51 +------------------------------------------
 1 file changed, 1 insertion(+), 50 deletions(-)

-- 
2.7.4

[PATCH 1/2] mtd: rawnand: denali: remove ->dev_ready() hook

[Masahiro Yamada]

The Denali NAND IP has no way to read out the current signal level
of the R/B# pin.  Instead, denali_dev_ready() checks if the R/B#
transition has already happened. (The INTR__INT_ACT interrupt is
asserted at the rising edge of the R/B# pin.)  It is not a correct
way to implement the ->dev_ready() hook.

In fact, it has a drawback; in the nand_scan_ident phase, the chip
detection iterates over maxchips until it fails to find a homogeneous
chip.  For the last loop, nand_reset() fails if no chip is there.

If ->dev_ready hook exists, nand_command(_lp) calls nand_wait_ready()
after NAND_CMD_RESET.  However, we know denali_dev_ready() never
returns 1 unless there exists a chip that toggles R/B# in that chip
select.  Then, nand_wait_ready() just ends up with wasting 400 msec,
in the end, shows the "timeout while waiting for chip to become ready"
warning.

Let's remove the mis-implemented dev_ready hook, and fallback to
sending the NAND_CMD_STATUS and nand_wait_status_ready(), which
bails out more quickly.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

 drivers/mtd/nand/raw/denali.c | 22 +---------------------
 1 file changed, 1 insertion(+), 21 deletions(-)

diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c
index f88a5dc..f069184 100644
--- a/drivers/mtd/nand/raw/denali.c
+++ b/drivers/mtd/nand/raw/denali.c
@@ -203,18 +203,6 @@ static uint32_t denali_wait_for_irq(struct denali_nand_info *denali,
 	return denali->irq_status;
 }
 
-static uint32_t denali_check_irq(struct denali_nand_info *denali)
-{
-	unsigned long flags;
-	uint32_t irq_status;
-
-	spin_lock_irqsave(&denali->irq_lock, flags);
-	irq_status = denali->irq_status;
-	spin_unlock_irqrestore(&denali->irq_lock, flags);
-
-	return irq_status;
-}
-
 static void denali_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
 {
 	struct denali_nand_info *denali = mtd_to_denali(mtd);
@@ -294,7 +282,7 @@ static void denali_cmd_ctrl(struct mtd_info *mtd, int dat, unsigned int ctrl)
 		return;
 
 	/*
-	 * Some commands are followed by chip->dev_ready or chip->waitfunc.
+	 * Some commands are followed by chip->waitfunc.
 	 * irq_status must be cleared here to catch the R/B# interrupt later.
 	 */
 	if (ctrl & NAND_CTRL_CHANGE)
@@ -303,13 +291,6 @@ static void denali_cmd_ctrl(struct mtd_info *mtd, int dat, unsigned int ctrl)
 	denali->host_write(denali, DENALI_BANK(denali) | type, dat);
 }
 
-static int denali_dev_ready(struct mtd_info *mtd)
-{
-	struct denali_nand_info *denali = mtd_to_denali(mtd);
-
-	return !!(denali_check_irq(denali) & INTR__INT_ACT);
-}
-
 static int denali_check_erased_page(struct mtd_info *mtd,
 				    struct nand_chip *chip, uint8_t *buf,
 				    unsigned long uncor_ecc_flags,
@@ -1349,7 +1330,6 @@ int denali_init(struct denali_nand_info *denali)
 	chip->write_byte = denali_write_byte;
 	chip->read_word = denali_read_word;
 	chip->cmd_ctrl = denali_cmd_ctrl;
-	chip->dev_ready = denali_dev_ready;
 	chip->waitfunc = denali_waitfunc;
 
 	if (features & FEATURES__INDEX_ADDR) {
-- 
2.7.4

[PATCH 2/2] mtd: rawnand: denali: remove denali_reset_banks()

[Masahiro Yamada]

In nand_scan_ident(), the controller driver resets every NAND chip.
This is done by sending NAND_CMD_RESET.  The Denali IP provides
another way to do the equivalent thing; if a bit is set in the
DEVICE_RESET register, the controller sends the RESET command to
the corresponding device.  denali_reset_banks() uses it to reset
all devices beforehand.

This redundant reset sequence was needed to know the actual number
of chips before calling nand_scan_ident(); if DEVICE_RESET fails,
there is no chip in that chip select.  Then, denali_reset_banks()
sets denali->max_banks to the number of detected chips.

As commit f486287d2372 ("mtd: nand: denali: fix bank reset function
to detect the number of chips") explained, nand_scan_ident() issued
Set Features (0xEF) command to all CS lines, some of which may not be
connected with a chip. Then, the driver would wait for R/B# response,
which never happens.

This problem was solved by commit 107b7d6a7ad4 ("mtd: rawnand: avoid
setting again the timings to mode 0 after a reset").  In the current
code, nand_setup_data_interface() is called from nand_scan_tail(),
which is invoked after the chip detection.

Now, we can really remove the redundant denali_nand_banks() by simply
passing the maximum number of chip selects supported by this IP
(typically 4 or 8) to nand_scan().  Let's leave all the chip detection
process to nand_scan_ident().

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

 drivers/mtd/nand/raw/denali.c | 29 -----------------------------
 1 file changed, 29 deletions(-)

diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c
index f069184..d1ae968 100644
--- a/drivers/mtd/nand/raw/denali.c
+++ b/drivers/mtd/nand/raw/denali.c
@@ -1040,29 +1040,6 @@ static int denali_setup_data_interface(struct mtd_info *mtd, int chipnr,
 	return 0;
 }
 
-static void denali_reset_banks(struct denali_nand_info *denali)
-{
-	u32 irq_status;
-	int i;
-
-	for (i = 0; i < denali->max_banks; i++) {
-		denali->active_bank = i;
-
-		denali_reset_irq(denali);
-
-		iowrite32(DEVICE_RESET__BANK(i),
-			  denali->reg + DEVICE_RESET);
-
-		irq_status = denali_wait_for_irq(denali,
-			INTR__RST_COMP | INTR__INT_ACT | INTR__TIME_OUT);
-		if (!(irq_status & INTR__INT_ACT))
-			break;
-	}
-
-	dev_dbg(denali->dev, "%d chips connected\n", i);
-	denali->max_banks = i;
-}
-
 static void denali_hw_init(struct denali_nand_info *denali)
 {
 	/*
@@ -1311,12 +1288,6 @@ int denali_init(struct denali_nand_info *denali)
 	}
 
 	denali_enable_irq(denali);
-	denali_reset_banks(denali);
-	if (!denali->max_banks) {
-		/* Error out earlier if no chip is found for some reasons. */
-		ret = -ENODEV;
-		goto disable_irq;
-	}
 
 	denali->active_bank = DENALI_INVALID_BANK;
 
-- 
2.7.4

Re: [PATCH 1/2] mtd: rawnand: denali: remove ->dev_ready() hook

[Miquel Raynal]

Hi Masahiro,

Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Fri,  7 Sep
2018 16:28:28 +0900:

> The Denali NAND IP has no way to read out the current signal level
> of the R/B# pin.  Instead, denali_dev_ready() checks if the R/B#
> transition has already happened. (The INTR__INT_ACT interrupt is
> asserted at the rising edge of the R/B# pin.)  It is not a correct
> way to implement the ->dev_ready() hook.
> 
> In fact, it has a drawback; in the nand_scan_ident phase, the chip
> detection iterates over maxchips until it fails to find a homogeneous
> chip.  For the last loop, nand_reset() fails if no chip is there.
> 
> If ->dev_ready hook exists, nand_command(_lp) calls nand_wait_ready()
> after NAND_CMD_RESET.  However, we know denali_dev_ready() never
> returns 1 unless there exists a chip that toggles R/B# in that chip
> select.  Then, nand_wait_ready() just ends up with wasting 400 msec,
> in the end, shows the "timeout while waiting for chip to become ready"
> warning.
> 
> Let's remove the mis-implemented dev_ready hook, and fallback to
> sending the NAND_CMD_STATUS and nand_wait_status_ready(), which
> bails out more quickly.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---

Both patches applied on nand/next.

Thanks,
Miquèl