linux-kernel - Re: [PATCH 4/4] perf: arm_spe: Enable ACPI/Platform automatic module loading

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Message-ID: <20190416135055.GA3313@fuggles.cambridge.arm.com>
Date:   Tue, 16 Apr 2019 14:50:55 +0100
From:   Will Deacon <will.deacon@....com>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, catalin.marinas@....com,
        rjw@...ysocki.net, lenb@...nel.org, mark.rutland@....com,
        sudeep.holla@....com, james.morse@....com,
        lorenzo.pieralisi@....com, linuxarm@...wei.com
Subject: Re: [PATCH 4/4] perf: arm_spe: Enable ACPI/Platform automatic module
 loading

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 <jeremy.linton@....com>
> > > Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> > > ---
> > >   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.
> 
> > 
> > > +	{ }
> > > +};
> > > +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
those, perhaps we can use the .id_table exclusively and drop the
.of_match_table instead?

Will