linux-kernel - Re: [PATCH v4 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller

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Date:   Sat, 22 Sep 2018 17:32:46 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     jianxin.pan@...ogic.com
Cc:     boris.brezillon@...tlin.com, linux-mtd@...ts.infradead.org,
        liang.yang@...ogic.com, yixun.lan@...ogic.com, dwmw2@...radead.org,
        computersforpeace@...il.com, marek.vasut@...il.com, richard@....at,
        jbrunet@...libre.com, Neil Armstrong <narmstrong@...libre.com>,
        carlo@...one.org, khilman@...libre.com, robh@...nel.org,
        jian.hu@...ogic.com, hanjie.lin@...ogic.com,
        victor.wan@...ogic.com, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] mtd: rawnand: meson: add support for Amlogic NAND
 flash controller

Hello,

On Thu, Sep 20, 2018 at 10:51 AM Jianxin Pan <jianxin.pan@...ogic.com> wrote:
[snip]
> +static int meson_nfc_clk_init(struct meson_nfc *nfc)
> +{
> +       int ret;
> +
> +       /* request core clock */
> +       nfc->core_clk = devm_clk_get(nfc->dev, "core");
> +       if (IS_ERR(nfc->core_clk)) {
> +               dev_err(nfc->dev, "failed to get core clk\n");
> +               return PTR_ERR(nfc->core_clk);
> +       }
> +
> +       nfc->device_clk = devm_clk_get(nfc->dev, "device");
> +       if (IS_ERR(nfc->device_clk)) {
> +               dev_err(nfc->dev, "failed to get device clk\n");
> +               return PTR_ERR(nfc->device_clk);
> +       }
> +
> +       nfc->phase_tx = devm_clk_get(nfc->dev, "tx");
> +       if (IS_ERR(nfc->phase_tx)) {
> +               dev_err(nfc->dev, "failed to get tx clk\n");
> +               return PTR_ERR(nfc->phase_tx);
> +       }
> +
> +       nfc->phase_rx = devm_clk_get(nfc->dev, "rx");
> +       if (IS_ERR(nfc->phase_rx)) {
> +               dev_err(nfc->dev, "failed to get rx clk\n");
> +               return PTR_ERR(nfc->phase_rx);
> +       }
neither the "rx" nor the "tx" clock are documented in the dt-bindings patch

> +       /* init SD_EMMC_CLOCK to sane defaults w/min clock rate */
> +       regmap_update_bits(nfc->reg_clk, 0,
> +                          CLK_SELECT_NAND | CLK_ALWAYS_ON | CLK_DIV_MASK,
> +                          CLK_SELECT_NAND | CLK_ALWAYS_ON | CLK_DIV_MASK);
clk_set_rate also works for clocks that are not enabled yet (except if
they have the flag CLK_SET_RATE_UNGATE)
this should help you to remove CLK_DIV_MASK here

is CLK_SELECT_NAND a bit that switches the clock output from the sdmmc
controller to the NAND controller?
if so: can this be modeled as a mux clock?

the public S905 datasheet doesn't mention CLK_ALWAYS_ON at bit 28 but
uses bit 24 instead. the description from the datasheet:
Cfg_always_on:
1: Keep clock always on
0: Clock on/off controlled by activities.
    Any APB3 access or descriptor execution will turn clock on.
Recommended value: 0

can you please explain what CLK_ALWAYS_ON does and why it has to be 1?


Regards
Martin