linux-kernel - Re: [PATCH v3 3/3] mtd: rawnand: denali: optimize timing parameters for data interface

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Date:   Mon, 18 Jun 2018 09:22:44 +0200
From:   Richard Weinberger <richard@....at>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-mtd@...ts.infradead.org,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Rob Herring <robh+dt@...nel.org>, linux-kbuild@...r.kernel.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        linux-kernel@...r.kernel.org, Marek Vasut <marek.vasut@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v3 3/3] mtd: rawnand: denali: optimize timing parameters for data interface

Am Freitag, 15. Juni 2018, 03:18:52 CEST schrieb Masahiro Yamada:
> This commit improves the ->setup_data_interface() hook.
> 
> The denali_setup_data_interface() needs the frequency of clk_x
> and the ratio of clk_x / clk.
> 
> The latter is currently hardcoded in the driver, like this:
> 
>   #define DENALI_CLK_X_MULT       6
> 
> The IP datasheet requires that clk_x / clk be 4, 5, or 6.  I just
> chose 6 because it is the most defensive value, but it is not optimal.
> By getting the clock rate of both "clk" and "clk_x", the driver can
> compute the timing values more precisely.

What datasheet do you have, is it public?
Mine clearly states that the factor is 4.
"The frequency of nand_x_clk is four times the frequency of nand_clk."

> To not break the existing platforms, the fallback value, 50 MHz is
> provided.  It is true for all upstreamed platforms.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Reviewed-by: Richard Weinberger <richard@....at>

Thanks,
//richard