linux-kernel - Re: [PATCH v2 2/2] serial: 8250_lpss: Switch to pcim_iomap() instead of pci_ioremap

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Message-ID: <YhYVl9YaoPDwAXO4@smile.fi.intel.com>
Date:   Wed, 23 Feb 2022 13:08:07 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 2/2] serial: 8250_lpss: Switch to pcim_iomap() instead
 of pci_ioremap_bar()

On Tue, Feb 22, 2022 at 08:02:10AM -0800, Christoph Hellwig wrote:
> 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.

So, what would be your suggestion for a) backportable change b) cleanup for
the current and future drivers?

-- 
With Best Regards,
Andy Shevchenko