linux-kernel - Re: [PATCH v3 3/5] driver core: platform: Add platform_put

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Message-ID: <4a7359bb-620b-2219-9b88-8a657f716336@huawei.com>
Date:   Thu, 26 Nov 2020 11:23:04 +0000
From:   John Garry <john.garry@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
        <lenb@...nel.org>, <rjw@...ysocki.net>,
        <gregkh@...uxfoundation.org>, <tglx@...utronix.de>,
        <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linuxarm@...wei.com>, <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v3 3/5] driver core: platform: Add platform_put_irq()

On 26/11/2020 09:28, Marc Zyngier wrote:
> On 2020-11-25 17:20, John Garry wrote:
>> Add a function to tear down the work which was done in platform_get_irq()
>> for when the device driver is done with the irq.
>>
>> For ACPI companion devices the irq resource is set as disabled, as this
>> resource is configured from platform_get_irq()->acpi_irq_get() and 
>> requires
>> resetting.
>>
>> Signed-off-by: John Garry <john.garry@...wei.com>
>> ---
>>  drivers/base/platform.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
>> index 88aef93eb4dd..3eeda3746701 100644
>> --- a/drivers/base/platform.c
>> +++ b/drivers/base/platform.c
>> @@ -289,6 +289,20 @@ int platform_irq_count(struct platform_device *dev)
>>  }
>>  EXPORT_SYMBOL_GPL(platform_irq_count);
>>

Hi Marc,

>> +void platform_put_irq(struct platform_device *dev, unsigned int num)
>> +{
>> +    unsigned int virq = platform_get_irq(dev, num);
> 
> I find it pretty odd to have to recompute the interrupt number,
> which in turn results in a domain lookup. 

Well we do have the virq available, but then we need to pass the virq 
and device irq index. But maybe I somehow reverse-lookup the ACPI res 
somehow from virq, such that we don't require the irq device index.

> It things were refcounted
> (they aren't yet), irq_dispose_mapping() would have no effect.
> 
> <pedant>
> It also goes against the usual construct where if you obtain an object
> based on some parameters, the release happens by specifying the object
> itself, and not the parameters that lead to the object.
> </pedant>

Yes, ideally we can use virq.

> 
>> +
>> +    irq_dispose_mapping(virq);
>> +    if (has_acpi_companion(&dev->dev)) {
>> +        struct resource *r = platform_get_resource(dev, IORESOURCE_IRQ,
>> +                               num);
>> +
>> +        if (r)
>> +            acpi_dev_irqresource_disabled(r, 0);
> 
> It looks to me that the ACPI thing is what needs to be promoted to a
> first class function, releasing all the resources that have used by
> a given device.

This is just clearing the irq resource flags, but it could be reasonable 
(to promote).

Thanks,
John