linux-kernel - Re: [PATCH RFC 05/15] ims-msi: Add mask/unmask routines

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Date:   Sun, 3 May 2020 17:16:18 -0700
From:   "Dey, Megha" <megha.dey@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Dave Jiang <dave.jiang@...el.com>, vkoul@...nel.org,
        maz@...nel.org, bhelgaas@...gle.com, rafael@...nel.org,
        gregkh@...uxfoundation.org, hpa@...or.com,
        alex.williamson@...hat.com, jacob.jun.pan@...el.com,
        ashok.raj@...el.com, jgg@...lanox.com, yi.l.liu@...el.com,
        baolu.lu@...el.com, kevin.tian@...el.com, sanjay.k.kumar@...el.com,
        tony.luck@...el.com, jing.lin@...el.com, dan.j.williams@...el.com,
        kwankhede@...dia.com, eric.auger@...hat.com, parav@...lanox.com
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-pci@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH RFC 05/15] ims-msi: Add mask/unmask routines

Hi Thomas,

On 4/25/2020 2:49 PM, Thomas Gleixner wrote:
> Dave Jiang <dave.jiang@...el.com> writes:
>>   
>> +static u32 __dev_ims_desc_mask_irq(struct msi_desc *desc, u32 flag)
> 
> ...mask_irq()? This is doing both mask and unmask depending on the
> availability of the ops callbacks.

yes, should have called it __dev_ims_desc_mask_unmask_irq perhaps.
> 
>> +{
>> +	u32 mask_bits = desc->platform.masked;
>> +	const struct platform_msi_ops *ops;
>> +
>> +	ops = desc->platform.msi_priv_data->ops;
>> +	if (!ops)
>> +		return 0;
>> +
>> +	if (flag) {
> 
> flag? Darn, this has a clear boolean meaning of mask or unmask and 'u32
> flag' is the most natural and obvious self explaining expression for
> this, right?

will change it a more meaningful name next time around ..
> 
>> +		if (ops->irq_mask)
>> +			mask_bits = ops->irq_mask(desc);
>> +	} else {
>> +		if (ops->irq_unmask)
>> +			mask_bits = ops->irq_unmask(desc);
>> +	}
>> +
>> +	return mask_bits;
> 
> What's mask_bits? This is about _ONE_ IMS interrupt. Can it have
> multiple mask bits and if so then the explanation which I decoded by
> crystal ball probably looks like this:
> 
> Bit  0:  Don't know whether it's masked
> Bit  1:  Perhaps it's masked
> Bit  2:  Probably it's masked
> Bit  3:  Mostly masked
> ...
> Bit 31:  Fully masked
> 
> Or something like that. Makes a lot of sense in a XKCD cartoon at least.
> 

After a close look, we can simply do away with this mask_bits. Looks 
like a crystal ball will not be required next time around after all.

>> +}
>> +
>> +/**
>> + * dev_ims_mask_irq - Generic irq chip callback to mask IMS interrupts
>> + * @data: pointer to irqdata associated to that interrupt
>> + */
>> +static void dev_ims_mask_irq(struct irq_data *data)
>> +{
>> +	struct msi_desc *desc = irq_data_get_msi_desc(data);
>> +
>> +	desc->platform.masked = __dev_ims_desc_mask_irq(desc, 1);
> 
> The purpose of this masked information is?

serves no purpose, borrowed this concept from the PCI-msi code but is 
just junk here.  Will be removed next time around.

> 
> Thanks,
> 
>          tglx
>