linux-kernel - Re: [PATCH v2 3/5] clk: aspeed: Add platform driver and register PLLs

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Date:   Wed, 27 Sep 2017 16:13:30 +1000
From:   Joel Stanley <joel@....id.au>
To:     Andrew Jeffery <andrew@...id.au>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-clk@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Jeremy Kerr <jk@...abs.org>,
        Rick Altherr <raltherr@...gle.com>,
        Ryan Chen <ryan_chen@...eedtech.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 3/5] clk: aspeed: Add platform driver and register PLLs

On Mon, Sep 25, 2017 at 10:40 PM, Andrew Jeffery <andrew@...id.au> wrote:
> On Thu, 2017-09-21 at 13:56 +0930, Joel Stanley wrote:

>> +     /*
>> +      * Memory controller (M-PLL) PLL. This clock is configured by the
>> +      * bootloader, and is exposed to Linux as a read-only clock rate.
>> +      */
>> +     regmap_read(map, ASPEED_MPLL_PARAM, &val);
>> +     aspeed_clk_data->hws[ASPEED_CLK_MPLL] = aspeed_calc_pll("mpll", val);
>
> IIRC the calculation in aspeed_calc_pll() is appropriate for the AST2500, but
> not the AST2400.

Ah ha. I knew there was a reason why I created an ast2400_calc_pll. I
will add it back in in the previous patch so we can use it here.

>> +     /* Video Engine (ECLK) mux and clock divider */
>> +     hw = clk_hw_register_mux(NULL, "eclk_mux",
>> +                     eclk_parents, ARRAY_SIZE(eclk_parents), 0,
>> +                     scu_base + ASPEED_CLK_SELECTION, 2, 2,
>> +                     0, &aspeed_clk_lock);
>> +     aspeed_clk_data->hws[ASPEED_CLK_ECLK_MUX] = hw;
>> +     hw = clk_hw_register_divider_table(NULL, "eclk", "eclk_mux", 0,
>> +                     scu_base + ASPEED_CLK_SELECTION, 20, 3, 0,
>
> On the AST2500 it looks like this should start at bit 28 for 3 bits, not bit

Good catch. Fixed in v3.

> 20. Separately, I'm not sure how to interpret the AST2400 datasheet here -
> maybe it's similar but with different wording ("clock slow down" rather than
> "divisor"?).
>
>> +                     div_table,
>
> This doesn't seem to be correct. There's the problem of 0b000 and 0b001 mapping
> the same value of 2 for the AST2500, whose table then increments in steps of 1.
> The AST2400 mapping on the otherhand is multiples of 2 starting at 2, with no
> inconsistency for 0b000 vs 0b001.

Yep, we do use a different table for ast2400 vs ast2500. See
ast2400_div_table vs ast2500_div_table.

>
>> +                     &aspeed_clk_lock);
>> +     aspeed_clk_data->hws[ASPEED_CLK_ECLK] = hw;
>> +
>> +     /* P-Bus (BCLK) clock divider */
>> +     hw = clk_hw_register_divider_table(NULL, "bclk", "hpll", 0,
>> +                     scu_base + ASPEED_CLK_SELECTION, 0, 2, 0,
>
> Bit 0 in SCU08 is a 1-bit field "CPU/AHB clock dynamic slow down enable". BCLK
> is actually in SCU*D*8, but (perhaps confusingly) documented immediately below
> SCU*0*8.

Good catch. Fixed in v3.

Cheers,

Joel