linux-kernel - Re: [PATCH 3/6] perf/marvell : Odyssey LLC-TAD performance monitor support

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Message-ID: <ZNt8f1Ui13SoxOUT@FVFF77S0Q05N>
Date:   Tue, 15 Aug 2023 14:24:15 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Gowthami Thiagarajan <gthiagarajan@...vell.com>
Cc:     "will@...nel.org" <will@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        Bharat Bhushan <bbhushan2@...vell.com>,
        George Cherian <gcherian@...vell.com>,
        Linu Cherian <lcherian@...vell.com>
Subject: Re: [PATCH 3/6] perf/marvell : Odyssey LLC-TAD performance monitor
 support

On Sat, Aug 12, 2023 at 01:51:00PM +0000, Gowthami Thiagarajan wrote:
> > -----Original Message-----
> > From: Mark Rutland <mark.rutland@....com>
> > Sent: Friday, July 28, 2023 9:08 PM
> > To: Gowthami Thiagarajan <gthiagarajan@...vell.com>
> > Cc: will@...nel.org; linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; Sunil Kovvuri
> > Goutham <sgoutham@...vell.com>; Bharat Bhushan <bbhushan2@...vell.com>; George Cherian
> > <gcherian@...vell.com>; Linu Cherian <lcherian@...vell.com>
> > Subject: [EXT] Re: [PATCH 3/6] perf/marvell : Odyssey LLC-TAD performance monitor support
> > 
> > External Email
> > 
> > ----------------------------------------------------------------------
> > On Fri, Jun 30, 2023 at 05:33:48PM +0530, Gowthami Thiagarajan wrote:

> > > +static int tad_pmu_event_counter_add(struct perf_event *event, int flags)
> > > +{

> > > +	if (!event->attr.disabled)
> > > +		return -EINVAL;
> > 
> > Why?
> Just checks the default disabled attribute.

Why does it matter?

What's the problem with opening an event which is *not* disabled?

[...]

> > > +static int tad_pmu_probe(struct platform_device *pdev)
> > > +{
> > > +	struct device *dev = &pdev->dev;
> > > +	struct tad_region *regions;
> > > +	struct tad_pmu *tad_pmu;
> > > +	struct resource *res;
> > > +	u32 tad_pmu_page_size;
> > > +	u32 tad_page_size;
> > > +	u32 tad_cnt;
> > > +	int i, ret;
> > > +	char *name;
> > > +
> > > +	tad_pmu = devm_kzalloc(&pdev->dev, sizeof(*tad_pmu), GFP_KERNEL);
> > > +	if (!tad_pmu)
> > > +		return -ENOMEM;
> > > +
> > > +	platform_set_drvdata(pdev, tad_pmu);
> > > +
> > > +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > > +	if (!res) {
> > > +		dev_err(&pdev->dev, "Mem resource not found\n");
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	ret = device_property_read_u32(dev, "marvell,tad-page-size", &tad_page_size);
> > > +	if (ret) {
> > > +		dev_err(&pdev->dev, "Can't find tad-page-size property\n");
> > > +		return ret;
> > > +	}
> > > +
> > > +	ret = device_property_read_u32(dev, "marvell,tad-pmu-page-size",
> > > +				       &tad_pmu_page_size);
> > > +	if (ret) {
> > > +		dev_err(&pdev->dev, "Can't find tad-pmu-page-size property\n");
> > > +		return ret;
> > > +	}
> > 
> > Why do you think these properties are necessary?
> > 
> > These should almost certainly be provided by IO resources, and shouldn't need a
> > custom property.
> 
> IO resources don't provide all the information in this case. Need to vary these values
> at different boot times. So, kept these custom properties.

I think the only rason the information is missing is that your DT binding isn't quite right.

Later on you do:

+       for (i = 0; i < tad_cnt && res->start < res->end; i++) {
+               regions[i].base = devm_ioremap(&pdev->dev,
+                                              res->start,
+                                              tad_pmu_page_size);
+               if (IS_ERR(regions[i].base)) {
+                       dev_err(&pdev->dev, "TAD%d ioremap fail\n", i);
+                       return -ENOMEM;
+               }
+               res->start += tad_page_size;
+       }

... which means you're splitting one reg entry into multiple mappings, whereas
you could have multiple reg entries, one per TAD page.

Thanks,
Mark.