[PATCH] mtd: rawnand: gpmi: Fix setting busy timeout setting

[Miquel Raynal]

Hi Sascha,

s.hauer at pengutronix.de wrote on Mon, 13 Jun 2022 13:30:30 +0200:

> The DEVICE_BUSY_TIMEOUT value is described in the Reference Manual as:
> 
> | Timeout waiting for NAND Ready/Busy or ATA IRQ. Used in WAIT_FOR_READY
> | mode. This value is the number of GPMI_CLK cycles multiplied by 4096.
> 
> So instead of multiplying the value in cycles with 4096, we have to
> divide it by that value. Use DIV_ROUND_UP to make sure we are on the
> safe side, especially when the calculated value in cycles is smaller
> than 4096 as typically the case.
> 
> This bug likely never triggered because any timeout != 0 usually will
> do. In my case the busy timeout in cycles was originally calculated as
> 2408, which multiplied with 4096 is 0x968000. The lower 16 bits were
> taken for the 16 bit wide register field, so the register value was
> 0x8000. With 2970bf5a32f0 ("mtd: rawnand: gpmi: fix controller timings
> setting") however the value in cycles became 2384, which multiplied
> with 4096 is 0x950000. The lower 16 bit are 0x0 now resulting in an
> intermediate timeout when reading from NAND.
> 
> Fixes: b1206122069aa ("mtd: rawnand: gpmi: use core timings instead of an empirical derivation")
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>

Shouldn't we add a Cc: stable here?

> ---
>  drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
> index 0b68d05846e18..889e403299568 100644
> --- a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
> +++ b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
> @@ -890,7 +890,7 @@ static int gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
>  	hw->timing0 = BF_GPMI_TIMING0_ADDRESS_SETUP(addr_setup_cycles) |
>  		      BF_GPMI_TIMING0_DATA_HOLD(data_hold_cycles) |
>  		      BF_GPMI_TIMING0_DATA_SETUP(data_setup_cycles);
> -	hw->timing1 = BF_GPMI_TIMING1_BUSY_TIMEOUT(busy_timeout_cycles * 4096);
> +	hw->timing1 = BF_GPMI_TIMING1_BUSY_TIMEOUT(DIV_ROUND_UP(busy_timeout_cycles, 4096));
>  
>  	/*
>  	 * Derive NFC ideal delay from {3}:


Thanks,
Miquèl