On 02/06/20 12:37, Benjamin GAIGNARD wrote:
> On 6/2/20 11:31 AM, Valentin Schneider wrote:
>>> @@ -99,6 +100,8 @@ enum state {
>>>
>>> #define OVERRUN_ERROR_THRESHOLD 3
>>>
>>> +#define DCMI_MIN_FREQ 650000 /* in KHz */
>>> +
>> This assumes the handling part is guaranteed to always run on the same CPU
>> with the same performance profile (regardless of the platform). If that's
>> not guaranteed, it feels like you'd want this to be configurable in some
>> way.
> Yes I could add a st,stm32-dcmi-min-frequency (in KHz) parameter the
> device tree node.
>
Something like that - I'm not sure how well this fits with the DT
landscape, as you could argue it isn't really a description of the
hardware, more of a description of the performance expectations of the
software. I won't really argue here.
>>
>>> struct dcmi_graph_entity {
>>> struct v4l2_async_subdev asd;
>>>
>> [...]
>>> @@ -2020,6 +2042,8 @@ static int dcmi_probe(struct platform_device *pdev)
>>> goto err_cleanup;
>>> }
>>>
>>> + dcmi->policy = cpufreq_cpu_get(0);
>>> +
>> Ideally you'd want to fetch the policy of the CPU your IRQ (and handling
>> thread) is affined to; The only compatible DTS I found describes a single
>> A7, which is somewhat limited in the affinity area...
> If I move this code just before start streaming and use get_cpu(), would
> it works ?
>
AFAIA streaming_start() is not necessarily executing on the same CPU as the
one that will handle the interrupt. I was thinking you could use the IRQ's
effective affinity as a hint of which CPU(s) to boost, i.e. something like:
---
struct cpumask_var_t visited;
struct irq_data *d = irq_get_irq_data(irq);
err = alloc_cpumask_var(visited, GFP_KERNEL);
/* ... */
for_each_cpu(cpu, irq_data_get_effective_affinity_mask(d)) {
/* check if not already spanned */
if (cpumask_test_cpu(cpu, visited))
continue;
policy = cpufreq_cpu_get(cpu);
cpumask_or(visited, visited, policy->cpus);
/* do the boost for that policy here */
/* ... */
cpufreq_cpu_put(policy);
}
---
That of course falls apart when hotplug gets involved, and the effective
affinity changes... There's irq_set_affinity_notifier() out there, but it
seems it's only about the affinity, not the effective_affinity, I'm not
sure how valid it would be to query the effective_affinity in that
notifier.
> Benjamin
>>
>>> dev_info(&pdev->dev, "Probe done\n");
>>>
>>> platform_set_drvdata(pdev, dcmi);
>>> @@ -2049,6 +2073,9 @@ static int dcmi_remove(struct platform_device *pdev)
>>>
>>> pm_runtime_disable(&pdev->dev);
>>>
>>> + if (dcmi->policy)
>>> + cpufreq_cpu_put(dcmi->policy);
>>> +
>>> v4l2_async_notifier_unregister(&dcmi->notifier);
>>> v4l2_async_notifier_cleanup(&dcmi->notifier);
>>> media_entity_cleanup(&dcmi->vdev->entity);
