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SubjectRe: [PATCH v5 3/3] clk: meson: add sub MMC clock controller driver
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Hi Jerome,

On 2018/10/25 20:54, Jerome Brunet wrote:
> On Thu, 2018-10-25 at 19:48 +0800, Jianxin Pan wrote:
>> Hi Jerome,
>>
>> On 2018/10/24 17:01, Jerome Brunet wrote:
>>> On Thu, 2018-10-18 at 13:07 +0800, Jianxin Pan wrote:
>>>> From: Yixun Lan <yixun.lan@amlogic.com>
>>>>
>>>> The patch will add a MMC clock controller driver which used by MMC or NAND,
>>>> It provide a mux and divider clock, and three phase clocks - core, tx, tx.
>>>>
[...]
>>>>
>>>> -/* Would prefer clk_regmap_div_ro_ops but clashes with qcom */
>>>> +static void clk_regmap_div_init(struct clk_hw *hw)
>>>> +{
>>>> + struct clk_regmap *clk = to_clk_regmap(hw);
>>>> + struct clk_regmap_div_data *div = clk_get_regmap_div_data(clk);
>>>> + unsigned int val;
>>>> + int ret;
>>>> +
>>>> + ret = regmap_read(clk->map, div->offset, &val);
>>>> + if (ret)
>>>> + return;
>>>>
>>>> + val &= (clk_div_mask(div->width) << div->shift);
>>>> + if (!val)
>>>> + regmap_update_bits(clk->map, div->offset,
>>>> + clk_div_mask(div->width) << div->shift,
>>>> + clk_div_mask(div->width));
>>>
>>> This is wrong for several reasons:
>>> * You should hard code the initial value in the driver.
>>> * If shift is not 0, I doubt this will give the expected result.
>>
>> The value 0x00 of divider means nand clock off then read/write nand register is forbidden.
>
> That is not entirely true, you can access the clock register or you'd be in a
> chicken and egg situation.
>
>> Should we set the initial value in nand driver, or in sub emmc clk driver?
>
> In the nand driver, which is the consumer of the clock. see my previous comments
> about it.
>
> If your device (nand in your case) needs a (sane) clock before doing anything
> else, just call clk_set_rate() and enable it with clk_prepare_enable().
>
> Look at our MMC driver, this is the first thing done after registering the
> clocks.
>
> The controller does no care at all about the clock rate or state. It is up to
> the consumer to express their needs.
>
> On a more general note:
> I agree that having a 0 value for CLK_DIVIDER_ONE_BASED divider makes no sense.
> If you think this point needs to be addressed, please:
>
> * make separated generic patch
> * against driver/clk/clk-divider.c
> * addressing specifically CLK_DIVIDER_ONE_BASED dividers (not all, as your
> change does)
> * with some comments explaining the intent.
In our emmc driver, the CLK_DIV_MASK is hard coded before clock registering in meson_mmc_clk_init():
clk_reg |= CLK_DIV_MASK;
writel(clk_reg, host->regs + SD_EMMC_CLOCK);
It's hard coded In previous version of nand driver. I will drop the new ops.

In addition , Martin suggested in previous discussions that "sclk-div" could be used [0][1].
This divider is just like a "sclk-div" with sclk->hi->width ==0.


>
>>
>>>
>>>> +}
>>>
>>> Please drop this.
OK. Thank you.
>>>
>>>> +
>>>> +/* Would prefer clk_regmap_div_ro_ops but clashes with qcom */
>>>> const struct clk_ops clk_regmap_divider_ops = {
>>>> .recalc_rate = clk_regmap_div_recalc_rate,
>>>> .round_rate = clk_regmap_div_round_rate,
>>>> @@ -122,6 +139,14 @@ static int clk_regmap_div_set_rate(struct clk_hw *hw, unsigned long rate,
>>>> };
>>>> EXPORT_SYMBOL_GPL(clk_regmap_divider_ops);
>>>>
[...]
>>>> +
>>>> +static struct clk_regmap_mux_data mmc_clkc_mux_data = {
>>>> + .offset = SD_EMMC_CLOCK,
>>>> + .mask = 0x3,
>>>> + .shift = 6,
>>>> + .flags = CLK_DIVIDER_ROUND_CLOSEST,
>
> Missed that earlier
>
> This flag makes no sense for a mux.
> Anyway this particular mux should never round up has doing so would be unsafe.
> The clock provided to the nand or the eMMC should be the requested or lower.
>
OK, I will drop it. Thanks for your time.
>>>> +};
>>>> +
>>>> +static struct clk_regmap_div_data mmc_clkc_div_data = {
>>>> + .offset = SD_EMMC_CLOCK,
>>>> + .shift = 0,
>>>> + .width = 6,
>>>> + .flags = CLK_DIVIDER_ROUND_CLOSEST | CLK_DIVIDER_ONE_BASED,
>
> Same here, drop CLK_DIVIDER_ROUND_CLOSEST
OK, I will drop it. Thank you!
>
>>>> +};
>>>> +
>>>> +static struct meson_clk_phase_data mmc_clkc_core_phase = {
>>>> + .ph = {
>>>> + .reg_off = SD_EMMC_CLOCK,
>>>> + .shift = 8,
[...]
>
> .
>

[0] https://patchwork.kernel.org/patch/10607157/#22238243
[1]https://lore.kernel.org/lkml/CAFBinCCuqUmVNdwUm7WbkHy1eWvOA5oQ5FcOuytbYNbgGcXnRQ@mail.gmail.com/T/#u

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