linux-kernel - Re: [PATCH v3 3/4] i2c: designware: Use the correct name of device-managed function

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Date:   Wed, 17 Feb 2021 19:40:14 +0800
From:   Dejin Zheng <zhengdejin5@...il.com>
To:     Krzysztof Wilczyński <kw@...ux.com>
Cc:     corbet@....net, jarkko.nikula@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, mika.westerberg@...ux.intel.com,
        rric@...nel.org, helgaas@...nel.org, wsa@...nel.org,
        linux-doc@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/4] i2c: designware: Use the correct name of
 device-managed function

On Tue, Feb 16, 2021 at 06:46:01PM +0100, Krzysztof Wilczyński wrote:
Hi Krzysztof,
> Hi Dejin,
> 
> Thank you for all the changes, looks good!
> 
> You could improve the subject line, as it is very vague - what is the
> new function name more correct?  Was the other and/or the previous one
> not correct?  Seems like you are correcting a typo of sorts, rather than
> introducing a new function in this file.
>
If you have read the following commit comments, As you know, the
pci_alloc_irq_vectors() is not a real device-managed function. But
in some specific cases, it will act as an device-managed function.
Such naming will cause controversy, So In the case of need device-managed,
should be used pcim_alloc_irq_vectors(), an explicit device-managed
function. So the subject name is "Use the correct name of device-managed function".

> > Use the new function pcim_alloc_irq_vectors() to allocate IRQ vectors,
> > the pcim_alloc_irq_vectors() function, an explicit device-managed
> > version of pci_alloc_irq_vectors(). If pcim_enable_device() has been
> > called before, then pci_alloc_irq_vectors() is actually
> > a device-managed function. It is used here as a device-managed
> > function, So replace it with pcim_alloc_irq_vectors().
> 
> The commit is good, but it could use some polish, so to speak.
> 
> A few suggestions to think about:
> 
>   - What are we adding and/or changing, and why
>   - Why is using pcim_alloc_irq_vectors(), which is part
>     of the managed devices framework, a better alternative
>     to the pci_alloc_irq_vectors()
>   - And finally why this change allowed us to remove the
>     pci_free_irq_vectors()
> 
These are all explained by the device-managed function mechanism.

> > At the same time, simplify the error handling path.
> 
> The change simplifies the error handling path, how?  A line of two which
> explains how it has been achieved might help should someone reads the
> commit message in the future.
> 
To put it simply, if the driver probe fail, the device-managed function
mechanism will automatically call pcim_release(), then the pci_free_irq_vectors()
will be executed. For details, please see the relevant code.

> [...]
> >  	if (controller->setup) {
> >  		r = controller->setup(pdev, controller);
> > -		if (r) {
> > -			pci_free_irq_vectors(pdev);
> > +		if (r)
> >  			return r;
> > -		}
> >  	}
> >  
> >  	i2c_dw_adjust_bus_speed(dev);
> > @@ -246,10 +244,8 @@ static int i2c_dw_pci_probe(struct pci_dev *pdev,
> >  		i2c_dw_acpi_configure(&pdev->dev);
> >  
> >  	r = i2c_dw_validate_speed(dev);
> > -	if (r) {
> > -		pci_free_irq_vectors(pdev);
> > +	if (r)
> >  		return r;
> > -	}
> >  
> >  	i2c_dw_configure(dev);
> >  
> > @@ -269,10 +265,8 @@ static int i2c_dw_pci_probe(struct pci_dev *pdev,
> >  	adap->nr = controller->bus_num;
> >  
> >  	r = i2c_dw_probe(dev);
> > -	if (r) {
> > -		pci_free_irq_vectors(pdev);
> > +	if (r)
> >  		return r;
> > -	}
> >  
> >  	pm_runtime_set_autosuspend_delay(&pdev->dev, 1000);
> >  	pm_runtime_use_autosuspend(&pdev->dev);
> > @@ -292,7 +286,6 @@ static void i2c_dw_pci_remove(struct pci_dev *pdev)
> >  
> >  	i2c_del_adapter(&dev->adapter);
> >  	devm_free_irq(&pdev->dev, dev->irq, dev);
> > -	pci_free_irq_vectors(pdev);
> 
> If pcim_release() is called should the pci_driver's probe callback fail,
Yes, you guessed right.

> and I assume that this is precisely the case, then all of the above make
> sense in the view of using pcim_alloc_irq_vectors().
> 
> Reviewed-by: Krzysztof Wilczyński <kw@...ux.com>
> 
> Krzysztof

BR,
Dejin