Hi Tero,
On Mon, Jan 4, 2016 at 8:36 AM, Tero Kristo <t-kristo@xxxxxx> wrote:
> On 01/01/2016 07:48 AM, Michael Turquette wrote:
>> Quoting Tero Kristo (2015-12-18 05:58:58)
>>> +static int _omap4_hwmod_clk_enable(struct clk_hw *hw)
>>> +{
>>> + struct clk_hw_omap *clk = to_clk_hw_omap(hw);
>>> + u32 val;
>>> + int timeout = 0;
>>> + int ret;
>>> +
>>> + if (!clk->enable_bit)
>>> + return 0;
>>> +
>>> + if (clk->clkdm) {
>>> + ret = ti_clk_ll_ops->clkdm_clk_enable(clk->clkdm,
>>> hw->clk);
>>> + if (ret) {
>>> + WARN(1,
>>> + "%s: could not enable %s's clockdomain %s:
>>> %d\n",
>>> + __func__, clk_hw_get_name(hw),
>>> + clk->clkdm_name, ret);
>>> + return ret;
>>> + }
>>> + }
>>> +
>>> + val = ti_clk_ll_ops->clk_readl(clk->enable_reg);
>>> +
>>> + val &= ~OMAP4_MODULEMODE_MASK;
>>> + val |= clk->enable_bit;
>>> +
>>> + ti_clk_ll_ops->clk_writel(val, clk->enable_reg);
>>> +
>>> + /* Wait until module is enabled */
>>> + while (!_omap4_is_ready(val)) {
>>> + udelay(1);
>>
>> This should really be a .prepare callback if you plan to keep the delays
>> in there.
>
> If this is changed to a .prepare, then all OMAP power management is
> effectively ruined as all clocks are going to be enabled all the time. hwmod
> core doesn't support .prepare/.enable at the moment that well, and changing
> that is going to be a big burden (educated guess, haven't checked this
> yet)... The call chain that comes here is:
>
> device driver -> pm_runtime -> hwmod_core -> hwmod_clk_enable / disable.
>
> The delay within this function should usually be pretty short, just to wait
> that the module comes up from idle.
Does it take multiple µs? Perhaps even one µs is much longer than needed?
> I recall the discussions regarding the udelays within clk_enable/disable
> calls, but what is the preferred approach then? Typically clk_enable/disable
> just becomes a NOP if it is not allowed to wait for hardware to complete
> transitioning before exiting the function.
FWIW, there are small loops with just a cpu_relax() in various clock drivers
under drivers/clk/shmobile/.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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