On Tue, Aug 26, 2014 at 11:54:43AM +0200, Arnd Bergmann wrote:

On Tuesday 26 August 2014 11:08:11 Thierry Reding wrote:

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On Tue, Aug 26, 2014 at 10:09:25AM +0200, Arnd Bergmann wrote:

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On Tuesday 26 August 2014 09:50:25 Thierry Reding wrote:

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On Tue, Aug 26, 2014 at 09:43:50AM +0200, Arnd Bergmann wrote:

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On Tuesday 26 August 2014 08:57:31 Thierry Reding wrote:

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On Mon, Aug 25, 2014 at 01:01:52PM -0600, Stephen Warren wrote:

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On 08/18/2014 11:08 AM, Andrew Bresticker wrote:

[...]

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+static int tegra_xusb_mbox_probe(struct platform_device *pdev)

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+    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+    if (!res)
+            return -ENODEV;

Should devm_request_mem_region() be called here to claim the region?

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+    mbox->regs = devm_ioremap_nocache(&pdev->dev, res->start,
+                                      resource_size(res));
+    if (!mbox->regs)
+            return -ENOMEM;

Is _nocache required? I don't see other drivers using it. I assume there's
nothing special about the mbox registers.

Most drivers should be using devm_ioremap_resource() which will use the
_nocache variant of devm_ioremap() when appropriate. Usually the region
will not be marked cacheable (IORESOURCE_CACHEABLE) and therefore be
remapped uncached.

Note that ioremap() and ioremap_nocache() are the same. We really shouldn't
ever call ioremap_nocache().

Perhaps we should remove ioremap_nocache() in that case. Or ioremap(),
really, and keep only those variants that do what they claim to do.

That would be good, but there are many instances of either one:

arnd at wuerfel:/git/arm-soc$ git grep -w ioremap | wc
   2156   13402  183732
arnd at wuerfel:/git/arm-soc$ git grep -w ioremap_nocache | wc
    485    2529   42955

Ugh... nothing that I currently have time for. Perhaps this is a good
one for the Janitors? I'm not sure if the kernelnewbies.org TODO list is
still frequented since many pages seem to be very old. Is there some
other place where I could add this?

I'm not sure if it's really worth it. One thing we might do is just
remove all definitions of ioremap_nocache and add a wrapper to
include/linux/io.h, to make it more obvious what is going on.

Yes, I suppose that would work too. I still think there's an advantage
in being explicit and avoid aliases like this. Perhaps a __deprecated
annotation would help with that?

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devm_ioremap_resource() and pci_iomap() checking for IORESOURCE_CACHEABLE is
rather silly, since it doesn't call ioremap_cache() in that case.

Then that should be fixed.

Yes. I'd suggest we just ignore that flag and always call ioremap here.

When I checked this before, IORESOURCE_CACHEABLE only ever gets set for
PCI ROM BARs, which we don't map into the kernel.

There's still a few users of ioremap_cache() around and they are
potential candidates for a conversion to devm_ioremap_resource(), so I
think it'd still make sense to keep the check.

Possibly. Note that these are all in architecture-specific code, as
evidenced by the fact that we have multiple names for this function:

ioremap_cache:    arm, arm64, x86, ia64, sh
ioremap_cached:   metag, unicore32
ioremap_cachable: mips

All other architectures have none of the above.

An alternative approach would be to kill off IORESOURCE_CACHEABLE
and introduce a devm_ioremap_resource_cache() helper when the first
driver wants it.

Looking briefly at the involved headers and structure there seems to be
quite a bit of potential for cleanup.

Thierry
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