Re: [PATCH v2 2/2] serial: 8250_lpss: Switch to pcim_iomap() instead of pci_ioremap_bar()

[Christoph Hellwig]

On Tue, Feb 22, 2022 at 10:14:16AM +0100, Jiri Slaby wrote:
> On 16. 02. 22, 9:53, Christoph Hellwig wrote:
> > On Tue, Feb 15, 2022 at 03:43:59PM +0200, Andy Shevchenko wrote:
> > > The pci_iounmap() doesn't cover all the cases where resource should
> > > be unmapped. Instead of spreading it more, replace the pci_ioremap_bar()
> > > with pcim_iomap() which uses managed resource approach.
> > 
> > pcim_iomap requires the use of ioreadX/iowriteX and thus runtime
> > overhead.  So in doubt please add a pcim_ioremap_bar instead of forcing
> > the legacy iomap/ioread/iowrite API onto modern drivers tht can't
> > support legacy port I/O.
> 
> Hmm, the driver combines pci_ioremap_bar with pci_iounmap. pci_iounmap does
> the right thing after all, but is that correct? And this driver is not
> alone, this shows more:
> git grep -E 'pci_iounmap|pci_ioremap_bar' `git grep -l pci_iounmap \`git
> grep -l pci_ioremap_bar\``

I think it is wrong.  It is not actively harmful unlike the the
combination of pci_iomap and then later use of accessors from the
ioremap family, but still not exactly a good idea.

In a perfect world we'd have some different annotation from __iomem
for the whole iomap family of functions.