Re: [PATCH 1/5] mtd: nand: lpc32xx_slc: fix calculation of timing arcs from given values

[Brian Norris <computersforpeace@gmail.com>]

+ Roland, who authored the driver

On Mon, Sep 28, 2015 at 07:38:58PM +0300, Vladimir Zapolskiy wrote:
> According to LPC32xx User's Manual all values measured in clock cycles
> are programmable from 1 to 16 clocks (4 bits) starting from 0 in
> bitfield. Correctness of 0 bitfield value (i.e. programmed 1 clock
> timing) is proven with actual NAND chip devices.
> 
> Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
> ---
>  drivers/mtd/nand/lpc32xx_slc.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mtd/nand/lpc32xx_slc.c b/drivers/mtd/nand/lpc32xx_slc.c
> index abfec13..5a3c6e0 100644
> --- a/drivers/mtd/nand/lpc32xx_slc.c
> +++ b/drivers/mtd/nand/lpc32xx_slc.c
> @@ -240,13 +240,13 @@ static void lpc32xx_nand_setup(struct lpc32xx_nand_host *host)
>  
>  	/* Compute clock setup values */
>  	tmp = SLCTAC_WDR(host->ncfg->wdr_clks) |
> -		SLCTAC_WWIDTH(1 + (clkrate / host->ncfg->wwidth)) |
> -		SLCTAC_WHOLD(1 + (clkrate / host->ncfg->whold)) |
> -		SLCTAC_WSETUP(1 + (clkrate / host->ncfg->wsetup)) |
> +		SLCTAC_WWIDTH(clkrate / host->ncfg->wwidth) |
> +		SLCTAC_WHOLD(clkrate / host->ncfg->whold) |
> +		SLCTAC_WSETUP(clkrate / host->ncfg->wsetup) |
>  		SLCTAC_RDR(host->ncfg->rdr_clks) |
> -		SLCTAC_RWIDTH(1 + (clkrate / host->ncfg->rwidth)) |
> -		SLCTAC_RHOLD(1 + (clkrate / host->ncfg->rhold)) |
> -		SLCTAC_RSETUP(1 + (clkrate / host->ncfg->rsetup));
> +		SLCTAC_RWIDTH(clkrate / host->ncfg->rwidth) |
> +		SLCTAC_RHOLD(clkrate / host->ncfg->rhold) |
> +		SLCTAC_RSETUP(clkrate / host->ncfg->rsetup);
>  	writel(tmp, SLC_TAC(host->io_base));
>  }
>  

Hmm, I'm guessing this was done to ensure we didn't round down too much.
Perhaps this should be using DIV_ROUND_UP() instead, so we can get an
exact match where possible, but not set too low of a clock rate by
rounding down?

Brian