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SubjectRe: [PATCH v10 04/27] clocksource: Add a new timer-ingenic driver
Hi Thierry,

On Mon, Mar 4, 2019 at 1:22 PM, Thierry Reding
<thierry.reding@gmail.com> wrote:
> On Sat, Mar 02, 2019 at 08:33:50PM -0300, Paul Cercueil wrote:
> [...]
>> diff --git a/drivers/clocksource/ingenic-timer.c
>> b/drivers/clocksource/ingenic-timer.c
> [...]
>> +struct ingenic_tcu {
>> + const struct ingenic_soc_info *soc_info;
>> + struct regmap *map;
>> + struct clk *clk, *timer_clk, *cs_clk;
>> +
>> + struct irq_domain *domain;
>> + unsigned int nb_parent_irqs;
>> + u32 parent_irqs[3];
>> +
>> + struct clk_hw_onecell_data *clocks;
>> +
>> + unsigned int timer_channel, cs_channel;
>> + struct clock_event_device cevt;
>> + struct clocksource cs;
>> + char name[4];
>> +
>> + unsigned long pwm_channels_mask;
>> +};
>> +
>> +static struct ingenic_tcu *ingenic_tcu;
>
> Is there really a need for this? Seems like the only two reasons for
> why
> you keep this around are as pointed out below.
>
>> +void __iomem *ingenic_tcu_base;
>> +EXPORT_SYMBOL_GPL(ingenic_tcu_base);
>
> Same here.
>
>> +static u64 notrace ingenic_tcu_timer_read(void)
>> +{
>> + unsigned int channel = ingenic_tcu->cs_channel;
>> + u16 count;
>> +
>> + count = readw(ingenic_tcu_base + TCU_REG_TCNTc(channel));
>
> Can't yo do this via the regmap?

I could, but for the sched_clock to be precise the function must return
as fast as possible. That's the rationale behind the use of readw()
here.

That's also the reason why ingenic_tcu_base is global and exported, so
that the OS Timer driver can use it as well.

>> +
>> + return count;
>> +}
>> +
>> +static u64 notrace ingenic_tcu_timer_cs_read(struct clocksource
>> *cs)
>> +{
>> + return ingenic_tcu_timer_read();
>> +}
>
> And here you've got access to the struct clocksource *, from which you
> should be able to get at struct ingenic_tcu * using container_of.
>
> [...]
>> +static int __init ingenic_tcu_init(struct device_node *np)
>> +{
>> + const struct of_device_id *id =
>> of_match_node(ingenic_tcu_of_match, np);
>> + const struct ingenic_soc_info *soc_info = id->data;
>> + struct ingenic_tcu *tcu;
>> + struct resource res;
>> + void __iomem *base;
>> + long rate;
>> + int ret;
>> +
>> + of_node_clear_flag(np, OF_POPULATED);
>> +
>> + tcu = kzalloc(sizeof(*tcu), GFP_KERNEL);
>> + if (!tcu)
>> + return -ENOMEM;
>> +
>> + /* Enable all TCU channels for PWM use by default except channel 0
>> + * and channel 1.
>> + */
>> + tcu->pwm_channels_mask = GENMASK(soc_info->num_channels - 1, 2);
>> + of_property_read_u32(np, "ingenic,pwm-channels-mask",
>> + (u32 *)&tcu->pwm_channels_mask);
>> +
>> + /* Verify that we have at least two free channels */
>> + if (hweight8(tcu->pwm_channels_mask) > soc_info->num_channels -
>> 2) {
>> + pr_crit("ingenic-tcu: Invalid PWM channel mask: 0x%02lx\n",
>> + tcu->pwm_channels_mask);
>> + return -EINVAL;
>> + }
>> +
>> + tcu->soc_info = soc_info;
>> + ingenic_tcu = tcu;
>> +
>> + tcu->timer_channel = find_first_zero_bit(&tcu->pwm_channels_mask,
>> + soc_info->num_channels);
>> + tcu->cs_channel = find_next_zero_bit(&tcu->pwm_channels_mask,
>> + soc_info->num_channels,
>> + tcu->timer_channel + 1);
>> +
>> + base = of_io_request_and_map(np, 0, NULL);
>> + if (IS_ERR(base)) {
>> + ret = PTR_ERR(base);
>> + goto err_free_ingenic_tcu;
>> + }
>> +
>> + of_address_to_resource(np, 0, &res);
>> +
>> + ingenic_tcu_base = base;
>> +
>> + tcu->map = regmap_init_mmio(NULL, base,
>> &ingenic_tcu_regmap_config);
>> + if (IS_ERR(tcu->map)) {
>> + ret = PTR_ERR(tcu->map);
>> + goto err_iounmap;
>> + }
>> +
>> + tcu->clk = of_clk_get_by_name(np, "tcu");
>> + if (IS_ERR(tcu->clk)) {
>> + ret = PTR_ERR(tcu->clk);
>> + pr_crit("ingenic-tcu: Unable to find TCU clock: %i\n", ret);
>> + goto err_free_regmap;
>> + }
>> +
>> + ret = clk_prepare_enable(tcu->clk);
>> + if (ret) {
>> + pr_crit("ingenic-tcu: Unable to enable TCU clock: %i\n", ret);
>> + goto err_clk_put;
>> + }
>> +
>> + ret = ingenic_tcu_intc_init(tcu, np);
>> + if (ret)
>> + goto err_clk_disable;
>> +
>> + ret = ingenic_tcu_clk_init(tcu, np);
>> + if (ret)
>> + goto err_tcu_intc_cleanup;
>> +
>> + ret = ingenic_tcu_clocksource_init(tcu);
>> + if (ret)
>> + goto err_tcu_clk_cleanup;
>> +
>> + ret = ingenic_tcu_timer_init(tcu);
>> + if (ret)
>> + goto err_tcu_clocksource_cleanup;
>> +
>> + // Register the sched_clock at the very end as there's no way to
>> undo it
>> + rate = clk_get_rate(tcu->cs_clk);
>> + sched_clock_register(ingenic_tcu_timer_read, 16, rate);
>
> Oh wow... so you managed to nicely encapsulate everything and now this
> seems to be the only reason why you need to rely on global variables.
>
> That's unfortunate. I suppose we could go and add a void *data
> parameter
> to sched_clock_register() and pass that to the read() function. That
> way
> you could make this completely independent of global variables, but
> there are 73 callers of sched_clock_register() and they are spread all
> over the place, so sounds a bit daunting to me.

Yes, that's the main reason behind the use of a global variables.
Is there a way we could introduce another callback, e.g. .read_value(),
that would receive a void *param? Then the current .read() callback
can be deprecated and the 73 callers can be migrated later.

>> +
>> + return 0;
>> +
>> +err_tcu_clocksource_cleanup:
>> + ingenic_tcu_clocksource_cleanup(tcu);
>> +err_tcu_clk_cleanup:
>> + ingenic_tcu_clk_cleanup(tcu, np);
>> +err_tcu_intc_cleanup:
>> + ingenic_tcu_intc_cleanup(tcu);
>> +err_clk_disable:
>> + clk_disable_unprepare(tcu->clk);
>> +err_clk_put:
>> + clk_put(tcu->clk);
>> +err_free_regmap:
>> + regmap_exit(tcu->map);
>> +err_iounmap:
>> + iounmap(base);
>> + release_mem_region(res.start, resource_size(&res));
>> +err_free_ingenic_tcu:
>> + kfree(tcu);
>> + return ret;
>> +}
>> +
>> +TIMER_OF_DECLARE(jz4740_tcu_intc, "ingenic,jz4740-tcu",
>> ingenic_tcu_init);
>> +TIMER_OF_DECLARE(jz4725b_tcu_intc, "ingenic,jz4725b-tcu",
>> ingenic_tcu_init);
>> +TIMER_OF_DECLARE(jz4770_tcu_intc, "ingenic,jz4770-tcu",
>> ingenic_tcu_init);
>> +
>> +
>> +static int __init ingenic_tcu_probe(struct platform_device *pdev)
>> +{
>> + platform_set_drvdata(pdev, ingenic_tcu);
>
> Then there's also this. Oh well... nevermind then.

The content of ingenic_tcu_platform_init() could be moved inside
ingenic_tcu_init(). But can we get a hold of the struct device before
the
probe function is called? That would allow to set the drvdata and regmap
without relying on global state.

>> +bool ingenic_tcu_pwm_can_use_chn(unsigned int channel)
>> +{
>> + return !!(ingenic_tcu->pwm_channels_mask & BIT(channel));
>> +}
>> +EXPORT_SYMBOL_GPL(ingenic_tcu_pwm_can_use_chn);
>
> I wonder if we could make this slightly nicer, though. Judging by the
> name, this one seems like it would only ever be used by the PWM. If
> the
> PWM is a child of the TCU, could it not pass in a struct device * that
> points to its parent into this? Or perhaps pass its own struct device
> *
> and have this function look up the struct ingenic_tcu from that?
> Should
> be something trivial as:
>
> bool ingenic_tcu_pwm_can_use_channel(struct device *dev, unsigned
> int channel)
> {
> struct ingenic_tcu *tcu = dev_get_drvdata(dev->parent);
>
> return !!(tcu->pwm_channels_mask & BIT(channel));
> }
>
> Thierry

Yes, that definitely looks better. Thanks for the hint.

-Paul


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