On Tue, Feb 11, 2014 at 03:30:33PM -0600, Rob Herring wrote:
> On Tue, Feb 11, 2014 at 12:29 PM, Geert Uytterhoeven
> <geert@xxxxxxxxxxxxxx> wrote:
> > On Tue, Feb 11, 2014 at 7:08 PM, Josh Cartwright <joshc@xxxxxxxxxxxxxx> wrote:
> >> It sure would be convenient if platform_device had a 'const struct
> >> of_device_id *of_id_entry' member similar to the existing struct
> >> platform_device_id one, that was set up during platform device matching.
> >> Most platform_driver users of of_match_node() would simply go away.
> >
> > Can't the entry be shared for both platform_device_id and of_device_id?
> > Only one of them can be valid at the same time, right?
> >
[..]
>
> I believe this is the reason drivers have to call of_match_device:
>
> commit b1608d69cb804e414d0887140ba08a9398e4e638
> Author: Grant Likely <grant.likely@xxxxxxxxxxxx>
> Date: Wed May 18 11:19:24 2011 -0600
>
> drivercore: revert addition of of_match to struct device
>
> Commit b826291c, "drivercore/dt: add a match table pointer to struct
> device" added an of_match pointer to struct device to cache the
> of_match_table entry discovered at driver match time. This was unsafe
> because matching is not an atomic operation with probing a driver. If
> two or more drivers are attempted to be matched to a driver at the
> same time, then the cached matching entry pointer could get
> overwritten.
>
> This patch reverts the of_match cache pointer and reworks all users to
> call of_match_device() directly instead.
>
> Signed-off-by: Grant Likely <grant.likely@xxxxxxxxxxxx>
Interesting, thanks for the history! I'm wondering if this same problem
exists for the existing platform_device_id cached pointer as well.
Okay, so maybe caching a pointer in the device isn't the best option,
what if we considered extending the platform_driver callbacks to include
a set of per-method (?) probe callbacks which do provide a handle to
matched identifiers.
In the case of a totally contrived platform_driver supporting ACPI, OF,
and !OF configurations, it might look something like:
static const struct of_device_id acme_of_table[] = {
/* ... */
{ },
};
MODULE_DEVICE_TABLE(of, acme_of_table);
static int acme_probe_of(struct platform_device *pdev,
const struct of_device_id *id)
{
/* ... */
return 0;
}
static const struct acpi_device_id acme_acpi_table[] = {
/* ... */
{ },
};
MODULE_DEVICE_TABLE(acpi, acme_acpi_table);
static int acme_probe_acpi(struct platform_device *pdev,
const struct acpi_device_id *id)
{
/* ... */
return 0;
}
static const struct platform_device_id acme_platform_table[] = {
/* ... */
{ },
};
MODULE_DEVICE_TABLE(platform, acme_platform_table);
static int acme_probe_acpi(struct platform_device *pdev,
const struct platform_device_id *id)
{
/* ... */
return 0;
}
static int acme_probe_name(struct platform_device *pdev)
{
/* ... */
return 0;
}
static struct platform_driver acme_driver = {
.probe_of = acme_probe_of,
.probe_acpi = acme_probe_acpi,
.probe_platform = acme_probe_platform,
.probe_name = acme_probe_name,
.remove = acme_remove,
.driver = {
.name = "acme",
.of_match_table = of_match_ptr(acme_of_table),
.acpi_match_table = ACPI_PTR(acme_acpi_table),
},
};
module_platform_driver(acme_driver);
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