linux-kernel - Re: [PATCH 7/9] ethernet: stmicro: Simplify PCI devres usage

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Message-ID: <ef48369d230ef1912da157e7b437040bece6b5f4.camel@redhat.com>
Date: Tue, 20 Aug 2024 09:52:40 +0200
From: Philipp Stanner <pstanner@...hat.com>
To: Andy Shevchenko <andy@...nel.org>
Cc: onathan Corbet <corbet@....net>, Jens Axboe <axboe@...nel.dk>, Wu Hao
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Subject: Re: [PATCH 7/9] ethernet: stmicro: Simplify PCI devres usage

On Mon, 2024-08-19 at 21:28 +0300, Andy Shevchenko wrote:
> On Mon, Aug 19, 2024 at 06:51:47PM +0200, Philipp Stanner wrote:
> > stmicro uses PCI devres in the wrong way. Resources requested
> > through pcim_* functions don't need to be cleaned up manually in
> > the
> > remove() callback or in the error unwind path of a probe()
> > function.
> > 
> > Moreover, there is an unnecessary loop which only requests and
> > ioremaps
> > BAR 0, but iterates over all BARs nevertheless.
> > 
> > Furthermore, pcim_iomap_regions() and pcim_iomap_table() have been
> > deprecated by the PCI subsystem in commit e354bb84a4c1 ("PCI:
> > Deprecate
> > pcim_iomap_table(), pcim_iomap_regions_request_all()").
> > 
> > Replace these functions with pcim_iomap_region().
> > 
> > Remove the unnecessary manual pcim_* cleanup calls.
> > 
> > Remove the unnecessary loop over all BARs.
> 
> ...
> 
> loongson_dwmac_probe()
> 
> > +	memset(&res, 0, sizeof(res));
> > +	res.addr = pcim_iomap_region(pdev, 0, pci_name(pdev));
> > +	if (IS_ERR(res.addr)) {
> > +		ret = PTR_ERR(res.addr);
> > +		goto err_disable_device;
> 
> It seems your series reveals issues in the error paths of .probe():s
> in many drivers...
> 
> If we use pcim variant to enable device, why do we need to explicitly
> disable it?

No.

> 
> >  	}
> 
> ...
> 
> loongson_dwmac_remove()
> 
> >  	pci_disable_msi(pdev);
> >  	pci_disable_device(pdev);
> 
> Not sure why we need these either...

It's complicated.

The code uses pciM_enable_device(), but here in remove
pci_disable_device().

pcim_enable_device() sets up a disable callback which only calls
pci_disable_device() if pcim_pin_device() has not been called.

This code doesn't seem to call pcim_pin_device(), so I think
pci_disable_device() could be removed.

I definitely would not feel confident touching pci_disable_msi(),
though. The AFAIK biggest problem remaining in PCI devres is that the
MSI code base implicitly calls into devres, see here [1]

P.

[1] https://lore.kernel.org/all/ee44ea7ac760e73edad3f20b30b4d2fff66c1a85.camel@redhat.com/