linux-kernel - Re: [PATCH 2/2] mtd: rawnand: denali: add more clocks

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Date:   Tue, 12 Jun 2018 19:36:06 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-mtd <linux-mtd@...ts.infradead.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Mark Rutland <mark.rutland@....com>, Rob Herring <robh@...nel.org>,
        Brian Norris <computersforpeace@...il.com>,
        DTML <devicetree@...r.kernel.org>,
        Richard Weinberger <richard@....at>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Rob Herring <robh+dt@...nel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Philipp Rosenberger <p.rosenberger@...utronix.de>,
        Richard Weinberger <richard@...ma-star.at>,
        David Woodhouse <dwmw2@...radead.org>,
        Marek Vasut <marek.vasut@...il.com>
Subject: Re: [PATCH 2/2] mtd: rawnand: denali: add more clocks

Maybe, the commit title should be:

mtd: rawnand: denali: add more clocks and improve setup_data_interface



2018-06-12 19:31 GMT+09:00 Masahiro Yamada <yamada.masahiro@...ionext.com>:
> According to the Denali User's Guide, this IP needs three clock inputs:
>
>  - clk: controller core clock
>
>  - clk_x: bus interface clock
>
>  - ecc_clk: clock at which ECC circuitry is run
>
> Currently, denali_dt.c requires a single anonymous clock and its
> frequency.  However, the driver needs to get the frequency of "clk_x"
> not "clk".  This is confusing because people tend to assume the
> anonymous clock means the core clock.
>
> Instead of the cheesy implementation, the clocks in the real hardware
> should be represented in the driver code and the DT-binding.
>
> I improved the ->setup_data_interface() hook as well.
>
> 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 specifies that clk_x / clk should be 4, 5, or 6.
> I just chose 6 because it is the most defensive value, but it is not
> very nice.  By getting the clock rate of both "clk" and "clk_x", the
> driver can compute the timing values more precisely.
>
> Adding new clocks would break the existing platforms.  For the backward
> compatibility, the driver still accepts the single clock just as before.
> Also, ->clk_rate and ->clk_x_rate are set to hardcoded values if clk_x
> is missing.
>
> It should work for all upstreamed platforms because Intel Moorestown,
> Altera (Intel) SOCFPGA, Socionext UniPhier use the following clock
> frequency:
>
>   clk = 50 MHz
>   clk_x = ecc_clk = 200 MHz
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---


-- 
Best Regards
Masahiro Yamada