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SubjectRe: [PATCH 4/4] perf: arm_spe: Enable ACPI/Platform automatic module loading

On 4/16/19 8:50 AM, Will Deacon wrote:
> On Thu, Apr 04, 2019 at 12:24:38PM -0500, Jeremy Linton wrote:
>> On 4/4/19 12:04 PM, Will Deacon wrote:
>>> On Tue, Mar 26, 2019 at 05:39:38PM -0500, Jeremy Linton wrote:
>>>> Lets add the MODULE_TABLE and platform id_table entries so that
>>>> the SPE driver can attach to the ACPI platform device created by
>>>> the core pmu code.
>>>> Signed-off-by: Jeremy Linton <>
>>>> Reviewed-by: Sudeep Holla <>
>>>> ---
>>>> drivers/perf/arm_spe_pmu.c | 11 +++++++++--
>>>> 1 file changed, 9 insertions(+), 2 deletions(-)
>>>> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
>>>> index 7cb766dafe85..ffa2c76c08bb 100644
>>>> --- a/drivers/perf/arm_spe_pmu.c
>>>> +++ b/drivers/perf/arm_spe_pmu.c
>>>> @@ -1176,7 +1176,13 @@ static const struct of_device_id arm_spe_pmu_of_match[] = {
>>>> };
>>>> MODULE_DEVICE_TABLE(of, arm_spe_pmu_of_match);
>>>> -static int arm_spe_pmu_device_dt_probe(struct platform_device *pdev)
>>>> +static const struct platform_device_id arm_spe_match[] = {
>>>> + { "arm,spe-v1", 0},
>>> It would be nice if we could avoid duplicating this string from the ACPI
>>> parsing code.
>> Ok sure, I just need to find a good common place for it.

There doesn't appear to be a good common place for this, so maybe
arm_pmu.h, which can then be included in the spe driver is the right thing.

>>>> + { }
>>>> +};
>>>> +MODULE_DEVICE_TABLE(platform, arm_spe_match);
>>>> +
>>>> +static int arm_spe_pmu_device_probe(struct platform_device *pdev)
>>>> {
>>>> int ret;
>>>> struct arm_spe_pmu *spe_pmu;
>>>> @@ -1236,11 +1242,12 @@ static int arm_spe_pmu_device_remove(struct platform_device *pdev)
>>>> }
>>>> static struct platform_driver arm_spe_pmu_driver = {
>>>> + .id_table = arm_spe_match,
>>>> .driver = {
>>>> .name = DRVNAME,
>>>> .of_match_table = of_match_ptr(arm_spe_pmu_of_match),
>>> Hmm, so some other drivers don't hook .id_table like you do, but instead
>>> hook .acpi_match_table in the driver structure. Is that not better?
>> This isn't actually an ACPI device, (aka not defined in the namespace), so
>> its missing much of the ACPI functionality. I think that also means its
>> needs to be declared this way.
> Looking at platform_match(), I'd really like to avoid having both an
> .id_table and an .of_match_table field.

> acpi_of_match_device() will actually use the .of_match_table, but it relies
> on ACPI_COMPANION returning a valid acpi_device. If we don't have one of

Right, via the fwnode it can cause an acpi DSDT defined device with a
_DSD "compatible" property to match an entry in the of_match_table
compatible string. I don't think this is us...

> those, perhaps we can use the .id_table exclusively and drop the
> .of_match_table instead?

This definitely made me do my homework, the following is AFAIK:

Its possible to match on just a .id_table, but this requires matching
the OF device name against the id_table name rather than against the OF
compatible string (*). This doesn't seem like a good idea, despite
platform_device_id entries being significantly smaller than the
of_device_id ones. Plus, I think we end up with two duplicate tables
because we still need the MODULE_TABLE(of,xxx) to assure that userspace
can associate the modalias with the module.

OTOH, it seems possible to match on module name directly
('arm_spe_pmu'), but this limits us to only a single device type for all
ACPI device variations unless we put platform checks in the module
itself (ick!). I suspect in the future if a spe.v2 were to come out this
would be a problem unless a separate module were created. Then there is
the fact this still needs a platform_device_id table, as the modalias
will read "platform:arm_spe_pmu". Which will cause people to question
why its not just assigned and matched against the .id_table.

*(interestingly trivia: There doesn't appear to be a single arm64 module
which matches on a MODULE_TABLE OF name. They only match type or
compatible. Out of the 3534 modules on my machine only three do any OF
table type matching, ipmi_si and two drivers for freescale networking
fsl_pq_mdio and gianfar_driver. In those cases, i'm not even sure its
actually necessary.)

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