linux-kernel - Re: [PATCH 02/16] mtd: nand: sunxi: fix clk rate calculation

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Date:	Tue, 8 Mar 2016 15:58:03 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-mtd@...ts.infradead.org, Chen-Yu Tsai <wens@...e.org>,
	linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 02/16] mtd: nand: sunxi: fix clk rate calculation

Boris,

On Mon,  7 Mar 2016 17:18:19 +0100, Boris Brezillon wrote:
> Unlike what is specified in the Allwinner datasheets, the NAND clock rate
> is not equal to 2/T but 1/T. Fix the clock rate selection accordingly.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> ---
>  drivers/mtd/nand/sunxi_nand.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/drivers/mtd/nand/sunxi_nand.c b/drivers/mtd/nand/sunxi_nand.c
> index 4d01e65..ab66d8d 100644
> --- a/drivers/mtd/nand/sunxi_nand.c
> +++ b/drivers/mtd/nand/sunxi_nand.c
> @@ -1208,13 +1208,7 @@ static int sunxi_nand_chip_set_timings(struct sunxi_nand_chip *chip,
>  	/* Convert min_clk_period from picoseconds to nanoseconds */
>  	min_clk_period = DIV_ROUND_UP(min_clk_period, 1000);
>  
> -	/*
> -	 * Convert min_clk_period into a clk frequency, then get the
> -	 * appropriate rate for the NAND controller IP given this formula
> -	 * (specified in the datasheet):
> -	 * nand clk_rate = 2 * min_clk_rate
> -	 */

When some HW works in a way that is *NOT* the one specified in the
datasheet, I think you should rather add *more* comments about this
aspect, rather than removing existing comments.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com